Dirt in Carbs?

krusty · January 21, 2016, 07:02:06 PM

Fired up the 4AY 1990 1200 a few nights ago to ride to a VJMC gathering at Harry's Cafe de Wheels in Newcastle. It hasn't been getting much use lately as I've been enjoying my 1100 since I got it registered.
It started easy enough in the usual manner. Full choke, hit starter and it runs. I went away to get my riding gear on while it warmed up but within, say, half a minute the revs went up to about 3000. The revs usually rise a little as it warms normally but this time it was quite sudden.
I knocked it back to half choke and all was ok, normal again. With my gear on I'm set to ride off and I normally shut the choke off completely and ride away. This time, as soon as I shut the choke off it stalled. Hmmm. Gave it a little choke and restarted, into gear and rode off down the street but all was not well. It was running rough as guts. Got to the main road at the end of our street and gave it some throttle and it accelerated really well but as soon as I backed off it went to running rough again. So I do a U turn and come back home and put it back in the garage. Swap to the 1100. All sweet.

So today I decide to have a look at it. I'm thinking there's some dirt got into the carbs but before I dive in I thought I should get some opinions and, possibly, eliminate any other problems.
Sorry this is a little long, are you still with me?
So today I decided to take notes on starting it up again. Here goes.
Ignition on, full choke, hit starter and it starts normally and is idling at 1500. After about half a minute it slowed to about 1200.
After about a minute I push the choke in slowly to about half way and the revs rise to 1800. I then pushed the choke in all the way and it stalled.
Restarted it with half choke and its idling on 1800. Push choke in to about one quater and idle dropped to 800 then within less than a minute it slows and stalls.
So, in short it wont start or idle without at least half choke. It also seems reluctant to restart unless I start pumping the throttle.
I then let it cool down and took the tank off with the idea of draining some fuel to look for any water contamination, there was none.
I also pulled the plugs. They were all barely finger tight which was a surprise as plugs usually need a little effort to 'crack' them free. The PO kept a log of its service and it showed these plugs have done almost 15000klm so time to replace. Took some pics of the plugs and they seem normal (considering the above). I replaced the plugs and nipped them up properly but it made no difference.
What's the consensus on plug type? My NGK book says DP8EA but it has DPR8EA in it. R=Delta ground electrode, is that significant.
Plugs are pictured 1-4 left to right.

krusty · January 21, 2016, 07:06:19 PM

Adding pics, again. oops, need to resize

movenon · January 21, 2016, 07:28:11 PM

Sounds like dirty pilot jets to me.

George

Pat Conlon · January 21, 2016, 08:23:49 PM

How old was the fuel? Did you try fresh fuel?

I don't know about the fuel you get down there...Does it have ethanol in it? (hopefully not) If it does have ethanol in it, don't store your bike with ethanol laced fuel, especially if you have the luxury of choice to buy non ethanol fuel.

Sounds typical of choke circuit and idle circuit obstructions. Time for r/r and cleaning. Pay attention to the fuel pick up point for choke circuit located at the bottom of the carb bowls along with the Pilot jets and needle jets (aka emulsion tubes, jet nozzles, etc)

How old is the fuel filter on your '90?

krusty · January 21, 2016, 08:58:42 PM

Quote from: Pat Conlon on January 21, 2016, 08:23:49 PM
How old was the fuel? Did you try fresh fuel?

I don't know about the fuel you get down there...Does it have ethanol in it? (hopefully not) If it does have ethanol in it, don't store your bike with ethanol laced fuel, especially if you have the luxury of choice to buy non ethanol fuel.

Sounds typical of choke circuit and idle circuit obstructions. Time for r/r and cleaning. Pay attention to the fuel pick up point for choke circuit located at the bottom of the carb bowls along with the Pilot jets and needle jets (aka emulsion tubes, jet nozzles, etc)

How old is the fuel filter on your '90?

Thanks for the tips.
I never use ethanol fuel. I use ULP95. Recently I started my 76 CB750F1 for the first time in over a year. Didn't add any fresh fuel. It fired up first stab on the button and idled happily. Same fuel.

oldktmdude · January 21, 2016, 09:33:01 PM

+1 pilot jets.

krusty · January 21, 2016, 09:42:31 PM

Diving in!
Now to get that airbox out.

Harvy · January 21, 2016, 10:01:44 PM

Quote from: krusty on January 21, 2016, 07:02:06 PM

What's the consensus on plug type? My NGK book says DP8EA but it has DPR8EA in it. R=Delta ground electrode, is that significant.
Plugs are pictured 1-4 left to right.

NGK DP8EA9 is the correct plug the "R" is a resistance plug and makes no difference - either will do...... the 9 on the end is the heat range.

Cheers
Harvy

Arnie · January 21, 2016, 10:03:14 PM

Yeah, I agree with Pete, pilot jets are clogged.

And, the "R" in the plug type stands for Resistor. Unless you have changed your ignition wires and caps, keep the R.
Your plugs look pretty carboned up, probably due to the choke being ON before you removed them.

Consider the value of your time vs the cost of UNI DualPod foam filters. They pay their way very quickly :-)

krusty · January 21, 2016, 10:13:38 PM

R = Resistor of course, thanks for pointing that out. Prefer to keep it stock. Looks like I don't have to remove the airbox to remove the carbs.
As I mentioned the plugs have done almost 15000klm which is their replacement interval according to my book. Haven't changed anything but this bike looks totally stock so I'll replace with same. I've only had this bike just under 12 months, it replaced another of same model and colour that was nicked.
Found this:
https://www.youtube.com/watch?v=CbWAAyz4mFc

Arnie · January 21, 2016, 10:23:11 PM

SuperCheap carries DPR8EA-9 plugs. They'll probably have a 20% off sale for AusDay if you can wait.

krusty · January 21, 2016, 10:51:08 PM

There's a Supercheap 5 mins up the road. It'll prolly take that long for me to do the carbs. Thanks

Bones · January 22, 2016, 12:54:31 AM

Quote from: krusty on January 21, 2016, 10:13:38 PM
Found this:
https://www.youtube.com/watch?v=CbWAAyz4mFc

Interesting to note in the video that he removed the throttle cables from the grip instead of the carbs,( seems easier) but he didn't lower the subframe and seemed to struggle a bit to get the carbs out ( harder). Like to see him getting them back in.

Its good to see how other people tackle things and if it seems easier adopt that practice. As the saying goes, work smarter not harder.

Earl Svorks · January 22, 2016, 01:12:31 AM

Krusty,
I didn't notice any mention of draining your float bowls. I would.Also,before you go to all the bother of carb r&r, it's simple to remove the mixture screws, the springs washers and "O"rings (After you've made sure to clean off the carb tops) A good shot of compressed air down each hole is often effective in clearing out the pilot jets.In the hundred times I've done this it has never caused any damage to a carb diaphram. If you do remove the carbs, you do know that lowering the rear subframe makes the job easier, right?

Harvy
The heat range is the 8, after the D.The -9 refers to the gap or tip design. At least that's what NGK would have us believe.

krusty · January 22, 2016, 01:20:03 AM

Jeez Earl, you've read my mind. As a matter of fact I have pulled the mixture screws and was about to post the question "Is it ok to use compressed air?". You just answered it.
I followed the procedure in the video but couldn't get the rack out and didn't want to force it so I've just left it loose for the moment. Besides it was too bloody hot out in the garage and my back was starting to play up.

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Dirt in Carbs?