Carb tuning help

[racerrad8]

I thought I might, but having read another FJ site, this chap felt the lack of support from the air box meant the carbs vibrated more, could lead to the manifolds splitting, and also you need to rig up a crankcase breather filter too, and that gets very oily. Thoughts? Experience? I am all for improvement, but I don't want to create myself some more problems.

I sell a more than five hundred RPM Dual Pod Foam Air Filter a year and I have never heard from a single customer of any intake cracking or breaking problem.

I also sell a ton of these, which work perfectly on the breather hose; RPM Breather Filter

Also, every Legend car running in the world today and over the last 22 years has never has an airbox to "support the carbs".

Finally in closing, the airbox offers minimal "support" to the carbs as the boots between the carbs & the air box are very thin and are a means of absorbing the movement/flex between the engine and the sub-frame for which the air box is rigid mounted.

Randy - RPM

[JohnnyW]

So, what might I have done wrong? I may have mixed up different carb parts, but I put new needles and seats in, so surely everything else is really not carb specific? I checked the float heights. I cleaned everything with carb cleaner, soaked the jets, and blew it all through with a compressor. I took my time. I followed the instructions on the sheet from Mr.Rafforth, along with a few other tutorials on the web.

What I am noticing now is that she fires first push, revs relatively high, then dies, and won't respond again until I have left it a while. I have an auxiliary fuel supply, gravity fed. but it does suggest that fuel 'gets through' somehow, burns off, then it doesn't get enough after that? When I could get it to kind of run previously (I have had the carbs off three time now!), it was very lumpy, and would only run on choke.

I am loathe to just take them off again, and do it all again, as it's such a wrestle to get the airbox etc back on, and mainly because I am just going over old ground. I suppose my question is what can I have done to make it so bad?

So, an update -

I have completely stripped them down again, twice, and in fact the float bowls three times
I have checked the new valve seats, they are 1.5mm as per a fuel pump model
I have checked, double checked and bloody triple checked the float heights - 22.4mm give or take 0.5mm
I have checked the floats aren't cracked
I have cleaned with carb cleaner, blown and dried every orifice I could with compressed air, ditto the jets
I have checked my new plugs are firing
I have cleaned and re-oiled my K&N standard replacement filter
I have checked both the airbox and inlet manifolds for leaks, at least visually, and can see none - The rubbers seem pliable and in good condition

The only progress I have made is that it runs for longer, but still requires the choke. As I let the choke in, it now revs spontaneaulsy to 4-5k before faltering, dropping back to say 1500 on choke slightly open, but kind of hunting/lumpy really. It will not really run without some choke.

I did think me being more careful with the float heights seemed to have helped a wee bit, but only thus far.

When I bench synched it, the butterflies were only a mil or so open

So I have checked the float heights, and have blown out the pilot/idle circuits. I have fuel, I have a spark.

What can I have done that is causing this?

The bike was running perfectly fine until the over-flowing carb led me to this strip down.....I just cannot see what I can have done, undone, re-done again?

I don't have the option of Randy at RPM, living in Scotland, (let alone the cost).

I am really fed up, and have spent over a man-week working on this. I am at a loss.

[JohnnyW]

I actually gave up on this and found a good mechanic. I lost a ton of nerves and it's better to give it to someone with far more experience than I have.

So did you let someone have a look at it Balky1? I am starting to think I will need to, but I wonder what thy're going to do differently?

[JPaganel]

Having the UNI pods makes the carb removal much less of a  task

Which it really isn't... I like the airbox. Mainly because I don't have to spend the money on jets and new filters. 

So I have checked the float heights, and have blown out the pilot/idle circuits. I have fuel, I have a spark.

When you measure float heights, are you measuring both sides of a float? If they are not even, you are going to have a ton of grief, as the actual level won't be what you think. I accidentally bent mine and found this out the hard way.

[JohnnyW]

Yep, measured both sides. Three were fine, but there was a small difference in one of the carbs, but I didn't want to bend it for fear of breaking it. One side was maybe 1mm higher than the other, but I set it at mid-way between the two, my reasoning being that the tolerance would cope with that. In hindsight, it may lead to a skewed lifting of the tang, but would that cause such an issue that I am having?

[copper]

You measure the float correctly http://www.fjowners.com/index.php?topic=9560.0

[racerrad8]

I just want to make sure you are measuring the floats level properly. If they are twisted, like you mentioned then you should straighten it out by gently twisting it back to flat and then setting the float level.

Here is some photos I have taken from my GYSM I posted many moons ago but I can't find them right now.







It might be worth check to see where you float level is externally to see if it is running out of fuel.




Now, I have to ask...You have completely disassembled the carbs; every jet, pilot screw, emulsion tube and everything else have been removed from the carb body with the exception of the throttle plate & shafts?

You have the new o-ring on the pilot mixture screw?
What are the mixture screws set to?

What jets are in the carbs now; Main, pilot & air bleed?

Just looking for an answer to your issue and that information will be the first stop.

Randy - RPM

EDIT: I see copper beat me to the float measuring part

[Pat Conlon]

Make sure you measure from the correct spot on the float.....the upper curved surface. See post #4: http://www.fjowners.com/index.php?topic=9560.0

[JohnnyW]

I just want to make sure you are measuring the floats level properly. If they are twisted, like you mentioned then you should straighten it out by gently twisting it back to flat and then setting the float level.

I realise I should have tried to have done that with the one slightly-off one now. I am pretty sure I did everything else as per your and various other tutorials

Now, I have to ask...You have completely disassembled the carbs; every jet, pilot screw, emulsion tube and everything else have been removed from the carb body with the exception of the throttle plate & shafts?

That's correct

You have the new o-ring on the pilot mixture screw?

Yes, except I have now taken them out and put them back twice more

What are the mixture screws set to?

3 turns

What jets are in the carbs now; Main, pilot & air bleed?

Whatever was standard FJ1200 3XW, I have had the bike since new. 110 main I know, not sure with the others

Just looking for an answer to your issue and that information will be the first stop.

Sure, I really appreciate the assistance

Randy - RPM

EDIT: I see copper beat me to the float measuring part

[mr blackstock]

G'day,
I read over the various posts and all the problems you are having.  I have an '85 FJ1100 with high mileage.  I did notice with mine that I had alot of trouble early on with idling etc.  I bought some nice cond. choke plungers and replaced my old ones.  Doing this improved the idle no end.  

My old choke plunger's rubber grommets had hardened oval, and when I reassembled the carbs after numerous attempts to clean them properly, I had placed the choke plungers back in differently, causing air leaks into the circuit.  thats when i bought better condition ones and it solved my problem.

A good way to see if you have a similar problem is look at the plungers when you disengage the choke at the handlebar, if they stick out or do not seat properly, that may be causing your odd running.

Also, RPM sell a replacement:
https://www.rpmracingca.com/proddetail.asp?prod=ChokePlunger
Also, fuel hose routing, mine was a bastard to get right!  I created easier pipe routing for my FJ.

[Pat Conlon]

Good tip on the carb plungers

Looking at the pictures of your fuel line routing, it appears that the right side branch line has a slight pinch where it joins carbs #3/4.
If you make those branch lines longer they will have less of a bend to them, resisting a pinch when the lines heat up. Then you could run the single fuel line (to the petcock) under the 2 branch lines like the oem route.

[JohnnyW]

Worth a try on the plungers. The collars didn't seem overly perished, but I am desperate now.......will let you know how I get on!

[mr blackstock]

G'day,

Yeah, after I took the pics I remember having to buy more pipe for a better fit.  The main reason I did it that way was to get more lift when removing the tank, it worked well with the pipe over the junction and not under.

JohnnyW: The rubber collars may not seem perished, but if they are rock hard, the brass plungers may have worn oval, using your finger slowely rotate and push in and out to find where the most resistance is, if any.

Also, on my bike the choke actuation rod that runs down the length of the carby bodies had worn into the carb body aluminium, making it difficult to actually use the choke.  maybe not a prob with yours, but a prick to fix.

Good luck, Gareth

[Alf]

Having the UNI pods makes the carb removal much less of a   task


I thought I might, but having read another FJ site, this chap felt the lack of support from the air box meant the carbs vibrated more, could lead to the manifolds splitting, and also you need to rig up a crankcase breather filter too, and that gets very oily. Thoughts? Experience? I am all for improvement, but I don't want to create myself some more problems.

On allusions  

My web is done for the use AND abuse of the FJs. I know personally 5 owners that go regularly on closed race tracks aboard their FJs, and in Mainland Spain still you can travel all day long between 160-200 km/h without too hassle in secondary roads (named "General roads" here).

By other side, in Spain the level of familiar incomes are not like on the US, Australia or UK. So it means that only a minority of us are owners of multiple motorbikes, and the typical FJ owner uses his only bike for everything: from daily workhorse to play races on weekends with more modern machinery, and in any kind of weather, from very hot in summer to snow in winter

For that kind of abuse I cant recommend individual filters. Test on yourself: without the air box support you can move the carbs up & down simply by hand. Imagine the forces with riding hard!

And with the airbox manifolds greased with red rubber grease the time to get out the carbs is near exactly the same that with individual filters

And like reliability is a must, I cant recommend to suppress the secondary oil circuit that go to the head (pic taken from Yamaha workshop manual)



In my favour, Practical Sportsbikes mag recommend like a general rule in 70-90 bikes fitting OE airbox if you want everything going sweet

[JohnnyW]

Cheers Alf. I had already been on your site, and had the same thoughts myself anyway, hence my comments above.

As I live in Scotland, and the weather is awful right now, the poor beast is sat in my garage looking very sorry for itself, awaiting me to get the energy to start to tackle it again.

I am still at the 'what the hell have I done wrong' stage, as I have checked, double checked, stripped and rebuilt countless times now, but still have the same problem.