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Stage 1, 3, or somewhere inbetween

  • Thread starter Thread starter richardhaggarty
  • Start date Start date
R

richardhaggarty

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I have a 1985 GS700. I have a set of K&N Pod filters and I switched the exhaust to an early '90's GSXR 1100 stock system. The bike refuses to start when the engine is cold (also seems worse when ambient air temperature is lower than 60F). Runs well once it gets started, occasional backfire and bogs slightly under Wide Open Throttle.

I rejetted the carbs with a Dynojet Kit based on the recommended Stage 3 settings; shimmed up jet needle, bigger main jet. I went with Stage 3 because I was assuming that while the GSXR exhaust in technically a stock system, it flows much more than my stock 700 setup.

Stock Carb Settings:
Main Jet: 122.5
Jet Needle: Untapered, Unshimmed

Current Settings:
Main Jet: 130.0
Jet Needle: Tapered, Shimmed up to 3rd position

I also have main jet sizes 114, 118, 125, 134 if anyone has any suggestions about a better setup.

Thanks for your help in advance, I am pulling the carbs right now to see what I can see.

Rich
 
The numbers on the Dynojets and the Mikuni jets mean different things. We need to know what type of jets you are reffering to.
 
Thanks for looking chef,

I didn't realize they used two different size conventions. However, all of the main jet sizes I gave are for the jets included in my Dynojet Kit, with the exception of the stock jets (122.5). I don't have the stock mains anymore; I only referenced those for informative purposes.

Since the other day I have stepped the mains down from 130 to 125. No luck solving the 'no cold start' problem there.

Last night I followed the Factory Service Manual through a Valve Clearance service. Two or three of the valves were too tight, but only by a thousandth of an inch or two. Still very reluctant to start when engine is cold.

Also, I had the carbs out last week to check for air leaks and the choke plungers. All seemed well.
 
The copper tube that runs from your carb body into your float bowl is where the choke picks up fuel. Make sure these are clear.
How is your compression numbers? Have checked valve clearance on the bike?
 
Last edited:
Did valve clearance last night. No go.

Fuel line is clear.

Compression tester I have doesn't fit.

Started easily with some starting fluid I bought. So that should relieve any concerns about bad spark or low compression.

I replaced the stock fuel valve with a a valve that doesn't have vacuum assist. Could this alone be the cause of the hard start condition? Seems like if that were the case I would also be starving for fuel when I go to WOT, which doesn't seem to be the case.

Is the fuel tank vented? So that when the fuel gets consumed there isn't a vacuum building up without the vacuum assist to relieve it?

Thanks chef
 
Yes, the gas cap has a vent. If clogged, fuel starvation will result. Same for the float bowls, they must vent correctly too.
Hard to say how the pipe will effect your flow/mixture. It may not allow the bike to run without issues beyond jetting. You can always try.
Your bikes symptoms suggest lean.
If I read you right, you say you have 130 DJ mains right now. Well, those are approx' the same as 122.5 Mikuni mains. If anything, a tad smaller.
The mains basically effect performance from 3/4 throttle to fully open. You can only test for the correct mains at those throttle positions, fully open being best. Plug reads after chopping off I would assume are whitish/lean. If so, I'd try something closer to Mikuni 150/155's. That would be allowing approx' 4-5 full sizes up (a full size = 5, a step = 2.5) for the K&N's and a couple full sizes for the pipe, IF, it really does flow better. Depends on those reads really.
You said the jet needles are set to the recommended settings but you're using a jet kit that's not designed for that pipe. So the base settings don't mean much. You need to mark your throttle grip and housing and do some solid 1/3 throttle position chop tests to see what the plugs say. Do what the plugs say.
For the pilot circuit, you'll need a larger pilot jet, at least. A full size up is a good starting point. Then adjust the mixture screws for best rpm.
The carbs must be vacuum synched to get accurate plug/performance reads. Float levels must be correct too. Test the pilot circuit at minimal throttle positions, such as cruising around in 4th/5th gear at a steady 35/45 mph, uphill or level. Warm up completely, then go a couple miles, chop off and read.
Depending on your test results/throttle reponse, you may need (probably will) larger air jets, drill out the vacuum ports to the diaphragm chambers, etc.
Be careful when high speed testing please.
 
I'd try the needle as far up she can go first and then if that doesn't make it right go up about 2 jet sizes (which I'd do anyway). Also the idle mixture might take a bit of richening up (try another turn out). If you go up in jet size you may also lower the needle because the jet size effects the needle hight. Going up in jet size is the same as raising the needle to a point. Midrange and some low end is needle and top end is jet. It still sounds like you need GAS. :cool:
 
RobGS850L said:
If you go up in jet size you may also lower the needle because the jet size effects the needle hight. Going up in jet size is the same as raising the needle to a point.
Click to expand...
The main jet size doesn't effect the jet needle position. The jet needle will regulate flow at approx' 1/4 to 3/4 throttle positions on CV carbs. The tapered jet needle rises through the needle jet and once the opening between the jet needle and needle jet becomes larger than the main jet opening, then the main jet regulates flow. The smallest opening in the circuit regulates flow.
Don't confuse increasing main jet size as the same effect as raising the jet needle. They both have an independent job to do at specific throttle positions. There is naturally some point of overlap when transitioning from the pilot to jet needle to main circuit, but they each operate separately and are controlled by their respective jets.
 
Thanks for the all of the replies,

Because Keith said to keep an eye on the plugs I noticed that they are the D9EA, one step colder than the stock D8EA plugs. I replaced them with the stockers. While that didn't solve my cold start symptom it did improve the engine response throughout the throttle range.

Next, I want to do a real thorough timing check on my Dyna 2000 ignition. Also, some experimenting with the carbs as Keith and Rob suggested.

I'll keep at it and keep you posted.

Rich
 
Any resolution to this? Cold start trouble would seem to mean a lean condition. Did you do any more jet swappin'? Thinking about a GSXR pipe on my 700...
 
Based on what I've heard from folks who have installed these kits on various bikes - you probably ought to drop your needle down to stock or just 1 notch up. Usually unless you have done a lot of big modifications to the engine raising the needle too much doesn't work too well.

You might even want to work the carbs down to the stage 1 setting. The stock system, even from an 1100, won't flow as much as a tuned header will.

On a personal note, what was it like fitting that system to your 700? I'm looking at pipe options for my '85 700.
 
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