Before I cleaned the carbs my FJ1200 engine was hard to start and ran poorly. Now it starts and idles fine but it spits back through the carbs when running above idle. The problem is most obvious on two of the four cylinders. The problem may have existed before I cleaned the carbs but it ran so bad overall that I didn't notice.
My problem is that I don't understand the spitting problem. It is more likely a carb problem or could the valves need adjustment? Can ignition problems cause carb spitting?
I've never worked on an engine with multiple carbs before. Could spitting be caused by incorrectly balanced carb adjustments?
Any thoughts/comments are appreciated.
Thanks!
sounds to me like you still have some blockages in the carbs.
did you clean all the little pin holes in the sides of the emulsion tubes ?
Nancy K was having similar problems with her FJ at the spring rally and once i got in there thats what was clogged up.
ran right as rain after a thorough cleaning.... you might even have to find a small piece of brass wire to physically clear the holes.
KOokaloo!
Clogged idle jets or an otherwise lean idle curcuit will cause the carbs to spit back through the intake. A bad (or cracked) spark plug can also cause spitting.
DavidR.
Thanks for your responses!
Since my original post I have cleaned the carbs two more times. They're so clean they could be approved by the FDA for food preparation. But the engine still spits back through all four the carbs and backfires out the exhaust. It starts and idles fine however.
When I say I "cleaned" the carbs here's what I mean. I removed all the bronze jets including the pilot jet that's located way down in a deep hole. I sprayed an entire can of carb cleaner through all the passages and made sure the tiny little holes in the throat of the carb and jets are perfectly clean. I originally thought the problem was the carbs but now I think it must be something else.
Since the engine idles ok I wonder if the spark advance is working. What happens if you rev up an engine and the advance is not working? The ignition is controlled by a TCI ignitor. But there's also another electronic box with a vacuum line that connects to the number two cylinder. That box apparently provides a signal to the TCI that is used to advance the timing. Could a lack of spark advance cause timing problems that result in spitting and backfiring?
What happens if the carbs are out of sync? Can that cause spitting?
Here's my game plan. I'm going to try to sync the carbs (I've never done it before). How critical is carb sync anyway? I thought syncing was just for fine tuning. Can it be off enough to cause spitting and backfiring?
I'm also going to troubleshoot the vacuum advance box. I have a diagram that shows the voltages that the box is supposed to produce with changes in pressure.
I'm also going to do a compression check. If the pressures are good can I be sure the valves are not leaking? Would the engine idle ok if the valves were leaking?
Hmm ... I just had another thought. I wonder if the fuel filter could be plugging up. Maybe it's allowing enough flow to keep the engine idling but not enough for higher speeds. The engine does run like it might be running out of gas. I'll put that on the list of things to check as well.
Any other thoughts or ideas are welcome.
If you've read this far, thanks for thinking about my problem!
Quote from: km4hr on September 02, 2011, 09:25:33 AM
Thanks for your responses!
Since my original post I have cleaned the carbs two more times. They're so clean they could be approved by the FDA for food preparation. But the engine still spits back through all four the carbs and backfires out the exhaust. It starts and idles fine however.
When I say I "cleaned" the carbs here's what I mean. I removed all the bronze jets including the pilot jet that's located way down in a deep hole. I sprayed an entire can of carb cleaner through all the passages and made sure the tiny little holes in the throat of the carb and jets are perfectly clean. I originally thought the problem was the carbs but now I think it must be something else.
Since the engine idles ok I wonder if the spark advance is working. What happens if you rev up an engine and the advance is not working? The ignition is controlled by a TCI ignitor. But there's also another electronic box with a vacuum line that connects to the number two cylinder. That box apparently provides a signal to the TCI that is used to advance the timing. Could a lack of spark advance cause timing problems that result in spitting and backfiring?
What happens if the carbs are out of sync? Can that cause spitting?
Here's my game plan. I'm going to try to sync the carbs (I've never done it before). How critical is carb sync anyway? I thought syncing was just for fine tuning. Can it be off enough to cause spitting and backfiring?
I'm also going to troubleshoot the vacuum advance box. I have a diagram that shows the voltages that the box is supposed to produce with changes in pressure.
I'm also going to do a compression check. If the pressures are good can I be sure the valves are not leaking? Would the engine idle ok if the valves were leaking?
Hmm ... I just had another thought. I wonder if the fuel filter could be plugging up. Maybe it's allowing enough flow to keep the engine idling but not enough for higher speeds. The engine does run like it might be running out of gas. I'll put that on the list of things to check as well.
Any other thoughts or ideas are welcome.
If you've read this far, thanks for thinking about my problem!
I would say carb synch is most likely your problem... multi-carb systems feeding different mixtures into their individual cylinders will cause the spitting/popping/backfiring/etc you describe. This behavior will also be different at different RPM levels and will be hard to track down. In my experience you need to be within a couple of cfm across the carbs to get even reasonable running behavior... then you focus on tuning your fuel delivery circuits.
Frank
Quote from: Flynt on September 02, 2011, 09:57:57 AM
I would say carb synch is most likely your problem... multi-carb systems feeding different mixtures into their individual cylinders will cause the spitting/popping/backfiring/etc you describe. This behavior will also be different at different RPM levels and will be hard to track down. In my experience you need to be within a couple of cfm across the carbs to get even reasonable running behavior... then you focus on tuning your fuel delivery circuits.
Frank
+1 on that Frank :good2:. Same with my experiences.
Hi
for some reason the bike is running lean, this is usually the cause of spitting back if you are confident that all the jets are perfectly clear then check that there are no air leaks anywhere if your bike has rubber covers on the little stubs you would use to connect the carb balance gauges to check these are OK also check there are no leaks on the vaccum pipes and check that the carb mounting rubbers are not cracked/ leaking this can be done by spraying them with wd40 when the engine is idling a change in engine speed indicates a leak
as racerman said you may need to use a strand of copper wire to clear the jets carb cleaner will take off mos crud but if the blockage is solid you may have to use a physical method
incidentally if you do a compression test and find that compression is down then put a small amount of oil,about 5cc in the affected bore and run the test again if the pressure rises its a problem with the piston/rings/bore if it doesn't then the problem is with the valves
Did you also remove the enricheners (chokes) and mixture screws and clean all those passages good? An air compressor is one of the best tools for carb cleaners you can own, they do great job of making sure all the passages are clear..... Canned carb cleaner is a distant 2nd.
^ I'd take an ultrasonic cleaner first :)
Sounds like an air leak someplace to me, but it's not gonna hurt to do a synch. There's a chance it's got slipped cam timing or something also, I suppose it depends on if it was running well recently or not, etc.
Hello everyone, thanks for your replies!
Since my last post I've tried most of your suggestions. So far no improvement. Carbs still spit and exhaust still backfires.
Like several people suggested I feel the carbs are too lean. But I don't know how to make them richer. The pilot mixture screws are currently turned out three full turns. I'm going to open them some more later today. I thought three turns should be plenty. Anybody know where theirs are set?
I cleaned the emulsion tube pin holes like Racerman suggested. But they already looked perfectly clean.
Should I try raising the jet needles in the sliders. Would that make it run richer? The spitting begins as soon as I crack open the throttle. I don't think the sliders have even moved by time the spitting begins.
Since my last post I synced the carbs. It was the first time I've ever done that. It smoothed out the idle but didn't help the spitting/backfiring problem. I got the manometer levels almost perfectly even on all cylinders with the throttles closed. But that raises a question, do you sync carbs with throttles completely closed or should the engine be idled up a bit?
I haven't removed/cleaned the enrichers (chokes) as Richbaker suggested. I've avoided separating the carbs from each other so far. I've been cleaning each one individually to avoid mixing the parts. Also, separating the carbs looks like it might create other problems. Maybe I should do it just for the sake of completeness.
BTW, what is the second vent tube for? Each carb has a bowl vent tube and a another vent tube. What does the second vent tube do?
I looked for air leaks but didn't find anything obvious. The rubber intake boots that the carbs plug into seem to be in good shape.
I also haven't tried using compressed air to clean the carbs as Richbaker suggested. I'll try that next. Carb cleaner sure flows through the passages just fine however.
Thanks again! Really appreciate your suggestions.
Is it just 2 cylinders spitting? Which cylinders are spitting?
Did you have the air pilot jet, idle jet and mixture screw out when you cleaned the idle circuit? Still sounds like a lean/clogged idle passage.
How old are the plugs?
DavidR.
Simple check if it'sthe pilot jets is to pull the choke out a LITTLE, and see if that stops the spitting.
It will raise your idle a little but it's a quick check.
Bob W
Quote from: km4hr on September 12, 2011, 08:36:34 AM
...
Like several people suggested I feel the carbs are too lean. But I don't know how to make them richer. ...
Did you check the float height on the spitters? angle of the dangle and all that..
Quote from: SlowOldGuy on September 12, 2011, 09:09:01 AM
Is it just 2 cylinders spitting? Which cylinders are spitting?
Did you have the air pilot jet, idle jet and mixture screw out when you cleaned the idle circuit? Still sounds like a lean/clogged idle passage.
How old are the plugs?
DavidR.
Number 1 & 2 cylinders spit more than 3 & 4. But I believe they all do it some. I can't tell which cylinders are backfiring however.
The plugs don't have many running hours on them. I'd say less than 20 hours.
Quote from: weymouth399 on September 12, 2011, 09:12:38 AM
Simple check if it'sthe pilot jets is to pull the choke out a LITTLE, and see if that stops the spitting.
It will raise your idle a little but it's a quick check.
Bob W
The spitting is reduced but not eliminated with the choke pulled out slightly. In fact that's about the only way the engine will even accelerate. Without any choke the engine idles beautifully and carbs sync perfectly. But open the throttles and the engine shuts off. A small amount of choke is required to make the engine speed up without a lot of pampering of the throttle.
Perhaps one way to make the carbs richer is to put more money into them. But that makes me poorer. :wacko3:
Quote from: ddlewis on September 12, 2011, 09:31:02 AM
Quote from: km4hr on September 12, 2011, 08:36:34 AM
...
Like several people suggested I feel the carbs are too lean. But I don't know how to make them richer. ...
Did you check the float height on the spitters? angle of the dangle and all that..
Unfortunately, I have forgotten to do that every I've removed the carbs for cleaning. Definitely need to do that however. But what are the chances that all four carbs have that problem?
Looks like I'll be removing the carbs again to blow out the ports with compressed air. I check float height then.
thanks
If you take them out, do yourself a favor and get 4 factory mikuni #40 pilot jets. You will be amazed how much better it will run. With a 155 air jet.
Bob W
Do you have a pipe on the bike? and what size pilots?
Quote from: weymouth399 on September 12, 2011, 10:54:28 AM
do yourself a favor and get 4 factory mikuni #40 pilot jets.
Bob W
+1
Quote from: weymouth399 on September 12, 2011, 10:54:28 AM
do yourself a favor and get 4 factory mikuni #40 pilot jets.
Bob W
Actually, the aftermarket jets with the external holes in the body are less susceptible to clogging and can be found here; Pilot Jet (http://www.rpmracingca.com/proddetail.asp?prod=Carb%3APilotjet)
Randy - RPM
Sorry I should have deleted that part from my quote.
I was pushing the larger #40, not the manufacturer.
Quote from: weymouth399 on September 12, 2011, 10:54:28 AM
If you take them out, do yourself a favor and get 4 factory mikuni #40 pilot jets. You will be amazed how much better it will run. With a 155 air jet.
Bob W
Bob,
I like your suggestion. Apparently others do too. I'm going to order the parts tomorrow.
I'll be ordering the jets from the RPM web site that Randy posted.
I discovered another interesting part on the RPM web site that could be relevant to my problem. RPM sells an O-ring kit. The kit includes "intake manifold O-rings". My engine doesn't have O-rings between the carbs and the intake manifold. Is it supposed to? My carbs fit very tight into the rubber intake manifold. Not sure why O-rings would be needed. Maybe the O-rings go between the intake manifold and the cylinder head. Anyway, maybe they are leaking and need to be checked, whereever they're located.
Here's a picture of the RPM O-ring kit: http://www.rpmracingca.com/proddetail.asp?prod=carbkit (http://www.rpmracingca.com/proddetail.asp?prod=carbkit)
BTW, my bike is actually a car. It's a retired Legends racecar. It hasn't been raced in years. It's mostly used for putting around a parking lot. It rarely runs much above idle which may be a problem itself. I assume the #40/155 jets will work in a Legends car.
I'm not trying to make the car run well at high speed. Just the opposite. I need it to run smoothly at low speed.
You guys are great! Thanks again for all the help.
Quote
I discovered another interesting part on the RPM web site that could be relevant to my problem. RPM sells an O-ring kit. The kit includes "intake manifold O-rings". My engine doesn't have O-rings between the carbs and the intake manifold. Is it supposed to? My carbs fit very tight into the rubber intake manifold. Not sure why O-rings would be needed. Maybe the O-rings go between the intake manifold and the cylinder head. Anyway, maybe they are leaking and need to be checked, whereever they're located.
You're correct. They're intake orings rather than carb orings. They fit between the rubber intakes and the head itself.
Quote from: Travis398 on September 12, 2011, 03:05:43 PM
Do you have a pipe on the bike? and what size pilots?
Quote from: weymouth399 on September 12, 2011, 10:54:28 AM
do yourself a favor and get 4 factory mikuni #40 pilot jets.
Bob W
+1
The bike is actually a car, a Legends race car. No longer used for racing. It only does light duty putting around parking lots, mostly running at or just above idle. It doesn't need high power or high performance. I just needs to run smoothly at low speed and growl when you goose it, but instead it sounds like a Fourth of July fireworks celebration.
Here's the latest news in the long saga about my FJ1200 engine. I installed #40 pilot jets as recommended by several readers. That seemed like a great idea but the carb spitting problem is still there. Now the engine is hard to start as well. It's apparently not getting enough gas, even with the choke on. It fires immediately when I spray carb cleaner into the carbs. Maybe the float levels are too low. Setting them is beyond my capability however.
I see places on the internet that sell carbs that have been overhauled and calibrated. If I knew that would fix the problem I'd consider laying down the cash. I don't want that expense without a solution however. I'm afraid something else is wrong like bad valves or an ignition problem.
I'm ready to admit defeat. I need a good mechanic in the Columbia,SC area. Any suggestions? Should I take it to a Yamaha dealer?
I'd pull the carbs and send them to Randy for a clean and overhaul.
Either that, or if it's just used as a toy hauler in a car park, new manifold and a Holley 350 single carb type of deal.
One thing that absolutely would fix it right up is bring it to a Rally.
Please forgive the dumb question. What is the symptom if the diaphragm/diaphragms are leaking ? When I rebuilt my carbs as a check I blew into the oblong hole feeding into the (actually below) diaphragm area and MUCH to my surprise 2 out of 4 leaked. The diaphragms did not have any holes in them, they they just would not seal good probably due to the age and crushing of the built in O ring seal.. I took each diaphragm cap and with some 400 grit sand paper and a flat surface "trued" up the caps. Still took a few tries to get them sealed.
At any rate if anyone rebuilds there carbs I would recommend the "blow" test. You should blow into them and have the slide snap right up.
And replacing the O rings between the plastic intakes and the head, I would call a must do while there. They are cheap and with a leaky one you could end up burning a hole in your piston or cyl..
Just passing along what I found with my carbs..
P.S. no comments on "blowing" your FJ :) good day
Quote from: Klavdy on February 14, 2012, 05:50:01 PM
I'd pull the carbs and send them to Randy for a clean and overhaul.
Either that, or if it's just used as a toy hauler in a car park, new manifold and a Holley 350 single carb type of deal.
One thing that absolutely would fix it right up is bring it to a Rally.
Interesting idea! Is a manifold such as the one you mentioned available?
Yes mate, I've seen one made by 'Lynx" , it was for a turbo application and of course there are a lot of other turbo adaptor manifolds for single carbs.
I dare say our mate Randy would know a fair bit more about the practical applications of one for a non turbo motor than I would but I reckon it would work pretty well for it's intended use.
Putting about the carparks etc as a toy hauler, plus you have the added benefit of body work to hide stuff behind.
Whaddya reckon Randy?
Where a loss of power is not an issue, would you use a single barrel Holley for easy , low speed drive-ability?
I know it goes against the grain, but for just cruising about the lot, this type of setup could be a goer, eh?
This may be an interesting build.
The diaphragms will slowly leak down during the blow test. There is no seal between the slide and the carb body, but it is a close fit, so pressure will slowly leak past the slide below the diaphragm. Another thing that will cause leakage during this test is the choke plunger. Make sure the rubber seal on the end of the choke plunger is in good shape, or make sure the plunger is all the way shut.
DavidR.
Have you checked your valve clearance? I would be looking at that and the plug wires
Scott
Quote from: ddlewis on September 12, 2011, 09:31:02 AM
Quote from: km4hr on September 12, 2011, 08:36:34 AM
...
Like several people suggested I feel the carbs are too lean. But I don't know how to make them richer. ...
Did you check the float height on the spitters? angle of the dangle and all that..
Is it possible that the fuel level in the bowls is correct at idle but not under load?
I've "cleaned" the carbs 5 or 6 times now, but I have not yet removed the floats and cleaned the needle valves. Could it be that the needle valves are partially plugged, allowing enough fuel for perfect idle but not enough to operate under load?
Also, the fuel pump seems to make plenty of pressure with the engine off. It spews out when I loosen the hose clamp at the carb. Do I need to measure the fuel pressure with a gage while the engine is running. How much pressure should there be?
The reason I haven't cleaned the needle valves is because it's hard to remove the floats. The carbs can be cleaned almost entirely without separating them from each other. But removing the float pins without separating the carbs is tough. I tried, it ain't easy. Separating the carbs seems like a pretty major operation. Is there another way?
Maybe I should open the bowl drains with the engine off and see how much flow I'm getting? If it just drips out then that's a problem right? There should be steady flow even after the bowls are empty, right?
I'm scared of the fuel supply system in this vehicle (Legends race car). It's electric fuel pump runs constantly. There's no low pressure cut off as far as I can tell. I'm afraid of getting a fire started with no way to shut the gas off. For that reason I don't want to do the bowl level test described in the Clymer's repair manual. That procedure involves attaching clear U-tubes to the bowl drains so you can view the level with the engine running. But if gas spills out of the tubes and a fire starts I might not be able to get to the ignition switch to shut it off. The procedure also requires removal of the carbs many times, not practical at all.
In summary, there is a possibility that the fuel flow is restricted inside the carbs between the fuel line attachment fitting and the needle valves. Is there an easy way to test this?
Sorry about the long post.
thanks!
Usually spitting indicates a lean condition, or a bad plug or plug wire.
If you can get the float bowls off, then removing the floats is easy. You do not need to separate the carbs to remove the float pins and floats. If it sat for any period of time (any probably even if it didn't) the filter screens on the end of the needle seat could be covered with old fuel gunk or other trash causing a restriction to fuel flow.
You have to remove the needle seat to get to the filter screen. Replace the needle seat o-rings while you're in there.
DavidR.