#2 and #4 not firing after rejet

[J_C]

When I got the bike #2 didn't fire. I ran a compression test and looked for spark, both seemed ok. Given the equation of 'Compression+spark+Fuel = Run' I assumed it had to be carb related.

Flash forward 1.5 months to today. The bike and I are celebrating our 26th bday and the completion of valve adjusting, carb cleaning, the addition of K&N pods, and rejetting. We decide to try and start it up. After turning it over a few times, 1 and 3 roar to life. 2&4 stay cold.

I jetted for use with an aftermarket exhaust pipe, which hasn't arrived yet. It will come next week. Could that be causing this problem? After the jetting I turned the screws to 2.75 out.

The only other thing of note is that carbs 2 and 4 were the ones that had to be replaced due to frozen screws, so I received carb bodies from road_clam and yogib. Might there be come kind of conflict even though they look identical?


Thank you thank you thank you.

 

[J_C]

Oh, and trying to answer the questions I know Keith would ask....

Float heights are all within spec, and the dynojet kit had me jet to 138 mains, needle on the 3rd notch down.

 

[KEITH KRAUSE]

Well, you shouldn't test the bike until all the parts are on that you jetted for.
But if it was just the jet kit parts causing a problem, it would figure all four cylinders wouldn't fire.
I'm sure you'll need to make jetting adjustments but I have to suspect the replacement carbs could have differences that are causing your problem. Can you verify what model they came off of and can you compare ALL jetting spec's to what your stockers are? Check the jets yourself too. The replacement carb bodies are also the same in number/position?
If positively the same, try a good bench synch. If it starts better, then vacuum synch.

 

[J_C]

Road_Clam has a 1982 Suzuki - GS1100EZ and Yogib has a 1985 GS1150ES. The bodies themselves are of the correct number and position.

I did check the jets when I took them out to put them in the carb cleaner and they were stock when i removed them.

I think the bench synch might be what I need to do. I completely forgot about it, thinking I'd just be able to do the vacuum synch. But you can't do that until it's firing.

In case anyone else was looking for a how-to on bench synching, I just found one. http://www.xs11.com/forum/showthread.php?threadid=88

I will do this next weekend when I get the pipes

 

[KEITH KRAUSE]

OK. Good luck with it. But I have to think there are significant jetting differences between an '85 1150 and your '80 1100. Even an '82 1100 would figure to have leaner factory jetting. Maybe a leaner needle jet or primary/pilot air jets, etc. An '85 1150 would figure to have even greater carburetion changes.

 

[J_C]

I just went out and bench synched it, but it didn't help.

Keith, I think you're probably right. But when I received the carb bodies, they were stripped (no jets etc) I replaced them with the parts from the broken (stock) carb bodies (Except for the air screws which were toast).

I am going to strip them back apart next weekend to double check, since I don't trust myself very much and I did receive a bunch of extra parts from yogib; I may have blindly used one.

I'll get with chef to find out exactly what I'm suppossed to have in there, since everything should be stock except mains/needles

 

[Billy Ricks]

Here are the specs for an '81 1100 and an '84 1150 just for comparison sake.
1981 1100 EX

Specs in mm.
Carb Type- Mikuni BS34SS
Bore Size-34 mm
ID# - 49200
Idle r/min - 1050 +/- 100 r/min
Fuel Level - 5.0 +/- 0.5
Float Height - 22.4 +/- 1.0
Main Jet - #107.5
Main Air Jet - 1.2
Jet Needle - 5D58
Needle Jet - X-1
Pilot Jet - #45
Bypass - 0.8, 0.8, 0.8
Pilot Outlet - 0.9
Valve Seat - 2.0
Starter Jet - #32.5
Pilot Screw -Pre-Set, Varies
Throttle Cable Play - 0.5-1.0

Type----------------- Mikuni BS36SS
I.D. NO. -------------00A10
Bore -----------------36mm
Idle r/min----------- 1100+or- 100r/min
Fuel level------------ 3.0 +- 0.5 mm
Float height---------- 21.4 +- 1.0 mm
Main jet ------------- #120(nos.1&4),#122.5(nos 2&3)
jet needle------------ 5D14
Needle jet ----------- X-3
Pilot jet ---------------#45
By pass--------------- 0.9,0.8,0.9 mm
pilot outlet------------ 0.9 mm
Valve seat------------ 2.0 mm
Starter jet------------ #32.5
Pilot screw------------ PRE-SET (2 turns back)
Throttle valve--------- #130
pilot air jet------------- #125
Throttle cable play-----2-3 mm
choke cable play-------0.5-1.0 mm

 

[J_C]

Thanks Billy, I'll need to recheck the numbers on all the jet parts.


Also, Looking at this...

could I make an educated guess and say that I should be looking critically at the pilot air screw and jet?

 

[Billy Ricks]

I hope this won't sound like a stupid question, but have you confirmed the carbs are getting fuel? It's possible the screen on the float seats are clogged.

 

[J_C]

Not a stupid question at all. When I'm behind the wrench, nothing is stupid :-D

The screens should be fine since I just cleaned them prior to changing the jets, but I did not check the bowls to see if they had fuel in them, though I was just thinking about going out there to do that. I'll remove the drain screw to ensure that fuel is at least getting to that point.

I did notice when I removed the carbs just now that the butterflies for one and three had a sheen of gas on them, but 2 and 4 were dry. Kind of makes sense though... if it's not firing it won't suck in fuel to the cylinder, correct?

 

[J_C]

Dumped the drains... Plenty of fuel came out so it's definetely not a stuck float valve

 

[Guest]

It doesn't sound like the bowls are as full as they should be. Try Raising the float 1mm at a time and see if you get gas flow. Do the 1150 with a 36mm carb have the same carb body?

 

[KEITH KRAUSE]

If you crank the motor, like trying to start it, fuel WILL wet the plugs if there's fuel entering the head. Keep the 2/4 plugs in but remove the caps. With no spark, the plugs at 2/4 should be wet after normal amount of cranking.
If no fuel on the plugs, you have to figure out why.
Back to Billy's carb info. It shows the 1150 carbs as 36mm and the 1100 as 34mm. You say you used two replacement carb bodies, but from which model?
If you used the 36mm, they'll never work right with your stock 34mm's.
If you did use 34mm replacements at both 2/4 and have identical jetting and all other tuning was identical, it sure is strange how the replacement carbs are the two that may not be supplying fuel?
As for that chart, the bike idles completely on the pilot circuit. At nearly closed throttle/normal 1,100 rpm idle, the pilot circuit will supply all the fuel needed to allow the bike to idle (after the choke circuit has helped it start from cold of course.)
Fuel enters the main jet and goes through a passage to and through the pilot jet. The fuel is then mixed with air coming from the pilot air jet located at the filter side/lower carb throat area. This mixture then goes through a passage that bypasses the throttle plate and enters the carb throat through tiny bypass ports. The mixture screw then regulates a second passage to the carb throat and this screw allows for fine tuning the correct mixture amount to each cylinder. Those tiny bypass ports must be very clean.

 

[J_C]

I thought the carb bodies looked identical, but i will follow up with both to double check that they were 34mm. When I get home from my business trip on the weekend I will check fuel on the plugs, then look at the pilot jets, since nothing else should really be affecting the idle. The floats were within spec, and the choke plungers all appear to be functioning correctly.

This is very frusterating

 

[KEITH KRAUSE]

I thought the carb bodies looked identical, but i will follow up with both to double check that they were 34mm. When I get home from my business trip on the weekend I will check fuel on the plugs, then look at the pilot jets, since nothing else should really be affecting the idle. The floats were within spec, and the choke plungers all appear to be functioning correctly.

This is very frusterating

Well, at least you're not alone. Give us the best info you can and we'll try to figure this out.
But if one or both of the carbs is actually 36mm, you need to replace them with 34mm. Should be easy to find out. Since you know who gave you what carbs and what bike they came off of?

 

[yogib]

Those are 34's you got from me,I did measure the venturi on them.Unfortunately they didn't put part#'s on the bodies off the 1100"s so I don't know the year they came from.My guess would be the bodies should be the same for 34mm 16 valve engines.I don't know for sure though.If there are differences the working parts would be different.It's got to be somthn' simple,gotta run for now stop back later.Don

 

[hungryman]

Not a stupid question at all. When I'm behind the wrench, nothing is stupid :-D

The screens should be fine since I just cleaned them prior to changing the jets, but I did not check the bowls to see if they had fuel in them, though I was just thinking about going out there to do that. I'll remove the drain screw to ensure that fuel is at least getting to that point.

I did notice when I removed the carbs just now that the butterflies for one and three had a sheen of gas on them, but 2 and 4 were dry. Kind of makes sense though... if it's not firing it won't suck in fuel to the cylinder, correct?

No, an air/fluel mixture should be delivered wether or not it's firing.

 

[yogib]

Are you SURE you have spark at both 2&4? The coil could be bad or the lead came off the coil.I'd double check JC.Don

 

[KEITH KRAUSE]

No, an air/fluel mixture should be delivered wether or not it's firing.

That's what I told him earlier Steve. I also told him the "sheen" he sees on the two wet throttle plates would be fuel coming out of the pilot circuit bypass ports. I described how the fuel gets to the bypass ports.
I'm thinking the two carbs that apparently aren't supplying fuel probably have dirty/clogged bypass ports. If the tiny ports ARE clean, then I'm thinking vacuum issue.

 

[J_C]

Thanks folks, I'll double check the coil and the bypass ports, though I definetely did see a blue spark when the ignition was on. Lots to do this weekend!

Not sure how the bypass ports would be clogged as I soaked them in carb cleaner for severals hours each, but I'll see if I can indetify them and blow some air through there