Need some help getting it running

[Cheriff]

Still working on getting my project back on the road, and I've finally reached the point that I know I need some help from the group. Here are some background details:

'88 1127
Pre-750 Carbs w/ factory pro jet kit (32.5 pilot, 15mm float height, 107 107 112.5 107 mains, 2.5 turns A/f screws)
Post 750 ignition system (including CDI)

At the settings above I can get it to idle if I am delicate with the choke and throttle. Once idling it is mostly responsive to the idle screw and will stumble and sound rougher when throttle is applied. Pulled the plugs and numbers 1 & 2 look fairly wet & a little dark and numbers 3 & 4 look normal.

My first thought is a need to try a vacuum sink which I will try to do as soon as I post this. Figured this is something that could make a 1 & 2 vs. 3 & 4 difference. I've tried some various things recently and 1 & 2 always seem to be more rich than 3 & 4. Infared thermometer confirms 1 & 2 are not firing as well as 3 & 4. Everytime I have had the carbs off and back on I would bench sink.

Bike has new engine intake boots and seals, and new rubbers on the airbox side also.

Stock electrical system which was running just fine before the project started...

I know there is more information I probably need to provide, but thats half the reason I wanted to start this thread. Need some input from some more experienced people.

[Wild-Bill]

The GSX1100G has the 1127 engine with the BST36SS carbs. Same as you have with a couple of differences that shouldn't matter.

Stock jets on it are:
Main: #120
Pilot: #30
Float height: 14.6mm +- 1mm

Your mains are small and the pilot jets are too big.

[Cheriff]

Thanks Bill. Know a year for that so I could look at ordering some parts?

Meanwhile, just hooked up the Morgan Carbtune II and it wasn't until about 4k that the slugs started bouncing around a little. That made me think there must be a vaccuum leak... So i started poking around with some starter fluid and a small straw and couldn't get it to rev up..

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Because I had them, I've tried the 37.5 pilots and it ran very rich (as expected, but I wanted to see the affect of something I did).. But even then 3 & 4 looked like they were burning most of it off, and 1 & 2 were thoroughly soaked.

Think of trying to swap plugs from 1/2 to 3/4.. Maybe those plugs are fouled.. If so I guess the problem will follow the plugs...

***************
Went back out.. Switched plugs around 1 to 4, 3 to 2. Started it up and noticed idle was a little higher than when I turned it off last. Now this time the carbtune slugs showed some movement - well all but #4. Played with synching the first three cylinders and it seemed to run more even, but still not inline 4 smooth. I did make sure that the vac line off of carb 4 was clamped off. Pulled the plugs afterward and they all looked much better. Plugs that were in 1 & 2 and now in 4 & 3 burned off some of the darkening on the ceramic part and 3 & 4 now in 1 & 2 did not look anywhere near as wet/dark as they had before....

Something odd for me was that the exhaust temp of 4 was still almost twice as high as the rest of the cylinders. The exhaust temp measurement were confirmed by handling the spark plugs - #4 much hotter than the rest.

After typing this and processing a little, it seems like there is a vac leak on #4... The vac leak prevents the carbtune from getting sufficient vacuum, and the oversize pilots make the other cylinders show slight wetness on plugs but on vac leak #4 it burns all that gas ok. Seem logical??

[Wild-Bill]

Re-read my earlier post. Your current pilots are oversized and your current mains are undersized. You've got jets for running a 750cc engine, not an 1100. I'm not saying that going with the stock sized jetting from Suzuki is the final answer but it'll at least get you in the ballpark. It might be worth talking to Factory Pro, too to see what differences exist between the kit you've got now and what they recommend for a GSX1100G. Basically, that's what you've got right now with the 1127 engine and 36mm carbs. (The 1100 Kat runs 34mm carbs.)

The Carbtune may be having trouble giving a reading simply because the engine's not running smoothly enough. While you've got the carbs out to swap those jets be sure you do a careful bench-sync to get yourself in the neighborhood.

Oh, and the GSX1100G was imported to the US from '91-'93. The bike hardly changed at all between those years.

[Cheriff]

Sorry Bill. I guess I focused on the "couple of differences that shouldn't matter" part. I was thinking that I should get those different parts for when it was time to start tuning, but that even with my current setup I should be able to get them running even across the cylinders. Thats how I interpreted it anyway..

Some other efforts I've tried have been to check to make sure all the little O-rings on the top of the carbs are in place (they are), various A/F settings, different pilot sizes, tried running with the airbox off to eliminate one possible vac leak spot (figured it would run poor but even across cylinders).... and with every attempt, cylinder four is still about twice as hot as the rest.

Potential problems I've thought of could be: valves (but I did set them before putting the motor in), partially clogged pilot jet/circuit (could be why with a 37.5 pilot and 3.5 turns out it plug #4 didnt look ridiculously wet), vac leak on the intake boot where it meets the motor.

[Wild-Bill]

Yeah, but the jetting definitely matters.
The most noticeable difference between BST36SS carbs setup for the G and the same carbs setup for a 750 Kat is that the G carbs only have one fuel line for all four carbs.

You're still running lean on #4 (or significantly leaner than the other three). With the jetting as far out as it is, it's even possible that #4 is about right and the rest are just running too rich to let the engine pull strongly. No telling. About the only thing you can tell for sure (at least in a forum like this) is that your jetting is jacked.

The good news is that you've got FP needles in there and FP uses Mikuni jets. The curve may be a little off for your engine but it should work. If you're still having trouble with the mid-range after getting the jetting where it's supposed to be then I'd contact FP to see if there's a different needle for the two applications. Alternatively, Arsenic may have those numbers on hand, too. Question to ask would be if the BST36SS jet kit has a different needle from the BST34SS kit.

[Cheriff]

Any good sources for ordering mikuni parts? Fast delivery and/or good price? Or just stick to the regular sources (BB, Ron Ayer, ect)?

Also think that because after just swapping plugs around it ran a little different its time to get some new ones so I can rule that out of the equation too.

[Kreylyn]

Any good sources for ordering mikuni parts? Fast delivery and/or good price? Or just stick to the regular sources (BB, Ron Ayer, ect)?

Also think that because after just swapping plugs around it ran a little different its time to get some new ones so I can rule that out of the equation too.

If your just buying a few jets, the local dealer should be able to get them cheap. If you don't have a local dealer and want a good selcection, try http://www.jetsrus.com/

Krey

[Wild-Bill]

Good prices. I've been going here: http://www.motorcyclecarbs.com

Edit:
Looked around jetsrus some more. The rest of their prices aren't as good and there isn't much love for Katanas or BST carbs in general.

[arsenic]

PJ Motorsports
You need Mikuni N100.604 Large Round Main Jet

[Wild-Bill]

Arsenic, now that you've checked in, do you happen to know if the FP jet needles are the same for the pre Kat750 and the GSX1100G?

[arsenic]

No, I don't have any idea, sorry.

[Wild-Bill]

Well, no help from that quarter. I looked it up and the 750 Kat had different stock needles from the GSX1100G. I think I'd make a call to FactoryPro. You may need new Needle Jets, Jet Needles Pilot Jets and Main Jets to get this thing running right. If that's the case, you're at the point where you may as well just order up a whole Stage 1 kit. Just be sure it's one for a GSX1100G so that you've got the parts to make 36mm carbs work with an 1127 engine.

[Cheriff]

Thanks guys. Easter got in the way a little but I'll get back into it tonight.

I suppose if a new FP kit is the answer I can probably sell this one I have to get some of the $ back.

[Cheriff]

Talked to FP. They say the needle shape is different for the 1127/36mm (GSX1100G) arrangement and the 750/36mm (GSX750F) setup. So it looks I need to get the other kit... Also, their kit uses the stock pilots, so I would need to order a set of 30's too.