1985 GS700ES carb jetting

[RASNDAS]

I recently aquired a 1985 GS700ES with a yoshimura exhaust and individual UNI pod style air filters. I believe the carbs are stock. The bike idles fine and has good wide open throttle power. The problem is it seems to have a bad lean surge at part throttle ( I can make it go away by pulling in the enrichener lever). I shimmed the needles up .070" and it still surges at 1/4 to 1/2 throttle. The surging is not quite as bad after full temperature is reached but is still annoying. I can raise the needles an additional .030" but that would be the limit. Main jet size is stock 122.5. Any suggestions

 

[hampshirehog]

IMHO this is the worst part of the throttle opening to get a problem. You're just leaving / left the pilot circuit and moving into the needle jet area. And in between is the slide cutaway. After having pfaffed around loads of time with slide cutaway and ruined loads of slides I wouldn't advise working on them.

You have started in the easiest (and cheapest) area - needle position. However, you say that your bike runs fine above this throttle range and that surprises me as you've fitted pods. Replacing the mains is the next area I'd look in - may be up a couple of sizes to start with, see if it road tests ok then start plug chopping. If it runs fine and the plugs show a rich spot in only one area I'd advise leaving there (just avoid running weak anywhere).

I've never found CVs easy to get running cleanly throughout the throttle range after fitting pods - by way of their operation, if you change one thing it effects other things. Best I've done is trial and error - usually one step forward two steps back:-s. Good luck.

Wally

 

[Guest]

I agree with going a little richer with the mains.

 

[RASNDAS]

Thanks Guys I will do that. I have never been real happy with PODS as 2 of my 18 bikes have them and both of them have carb issues. Is it possible to get a slightly thinner needle with roughly the same taper which would fatten up that area.

 

[Guest]

A Dyno-jet or Factory pro jet kit would have different needles. Plus they would have five grooves in them for height adjustment. I have a set of 34mm flat slide cv carbs from an '88 1100 gsxr on my '83 with a Dyno-jet stage 3 kit in them, with k/n pods and an early aluminum can style yosh pipe.

 

[KEITH KRAUSE]

If you're positive the problem is at 1/4 to 1/2 throttle, then your problem is the jet needle circuit.
There is some overlap with the pilot circuit at 1/4 but not any significant amount at 1/2. With .030" richer jet needle adjustment avialable, I'd try that unless your current SOLID 1/3 to 1/2 throttle tests/chops show very white plug colors still.
.022" equals approx' 1 full position richer so you still have a chance to richen it enough, depending on the current reads.
Just be sure the bike is in otherwise good tune and any issues you have are truly the fault of the jetting.
To get accurate plug/performance reads, you must vacuum synch too.
Mark the throttle housing and grip if any doubt as to true throttle position. Factor in throttle cable free play. Make 2, 1 mile runs (level or uphill ground is better) at solid 1/3 to 1/2 throttle, chop off and read. Unless the plugs show very white insulators, you have a chance with that .030" you still have.
As for the main, what is the stock main? Typical increases for your pipe/pod mods, are in the 20 (very minimum) to 35 range. So if you started with a "110" for example, you'd generally need a 130 to 145 in my opinion. If you're in higher elevation, drop 2.5 (1/2 size) to 5. I'd tend to try the richer end of that range and start with a 140 in THIS example. Test the main at full throttle.
In general, the best main is the main that gives you the best top speed when tested under identical conditions.

 

[KEITH KRAUSE]

Also, be sure you have no float bowl venting issues. The bowls must vent 100%. Pod filters can be greatly effected by less than perfect bowl venting. This symptom cannot be compensated by richening the jetting.
Poor bowl venting is most noticable at steady/cruising speeds from approx' 35 to 70 mph and even more sometimes. Feels a bit like the first sign of running low on fuel.
If your carbs have the 2 floatbowl vent lines, try removing them and re-test. Also, blow into the vents to see if the passages are clear. If any doubt they are 100% clear, then take things apart and verify. Flush with cleaner and high pressure air. I use 150 psi or so to really clean all carb passages.
I assume you're positive the floats are adjusted correctly too.

 

[TheCafeKid]

hey Keith i have a question for you but dont wanna jack so when ya get time can you check out our thread in the tech section?? Thanks!!

TCK

 

[KEITH KRAUSE]

hey Keith i have a question for you but dont wanna jack so when ya get time can you check out our thread in the tech section?? Thanks!!

TCK

Oh allright. I was just about to sign off but I'll go over there.
shuffle...shuffle...

 

[KEITH KRAUSE]

Not sure. Which thread?

 

[RASNDAS]

Thanks again guys. I wondered about the float bowl vwnting myself and shortened the hoses from the vents to end about where the filters are ( wanted to make sure they did not end in a low pressure are behind the engine). Didn't change the symptoms. I was a little surprised that the bike seemed to run so well on the top end with the stock main jets which are 122.5 I will put in a set of 145 and see what happens. I will also verify the float bowl vents are indeed clear. The symptom is just like you are starting to run out of gas and it persists even when I kick it down a gear and hold the same throttle setting so I don't think it is pipe related. The Carburetors have been throughly cleaned. and the valve lash adjusted. plugs are faily new ( less that 1000 miles). I will try your suggestions this weekend and let you know. It does seem hard to believe the main jet would influence the mixture ratio at 1/4 to1/2 throttle.

 

[LeeGS550E]

I am working on a similar situation with my 700 engine. I have emgo pods that breathe too much, as well as a vance&hines 4-1, and I have been backing down from the 140's that I tried first time around. I am now down to 135's, and am working out the same 1/4-1/2 throttle issue that you are. Sure, you could try the 145's as a test, but in my experience with these carbs, that will be much higher than you need to go.

 

[RASNDAS]

Thanks for the input. I just happen to have a set of 135's so I will start there. Any light you can shed on your fix will be greatly appreciated. I will be working on it this weekend and will post results.

 

[KEITH KRAUSE]

What IS the stock main size? My suggested range given was based on a 110 but was just an example. If you look at some stage 3 kits out there, most of them increase the mains about 6 full sizes (30) or even more. It's my opinion they are allowing at least a good 4 full sizes for the pods and 2 full sizes for a quality pipe. As always, some motors/mods flow better than others and thus the rather large range of jets that prove to be the best for your bike.
1/4 to 1/2 throttle position issues will have nothing to do with main jet choice but I only mentioned that the main seemed small to me.
As for the float bowl vent lines, if you are possibly experiencing poor venting and you verify the passages are clear, a true venting issue will NOT be helped or minimized by shortening the lines, even if you shorten them to just a couple inches. I've tried it myself in the past on several models. You have to remove the lines, period. I'm not saying you have this issue but if you even have a subtle amount of fuel starvation caused by poor venting, it will not be cured by shortening the lines. Your description of the symptom certainly fits a poor venting issue.

 

[KEITH KRAUSE]

And since venting is brought up, be sure your gas cap vent is 100% clear.
Many have blamed other things just to discover the cap is getting gummed up and causing or contributing to a problem.

 

[RASNDAS]

OK here is what I found out. Contrery to what the previous owner told me the main jets were 135's instead of the stock 122.5's which would account for the top end running good. I pulled the last of the washers off of the needle which now means the needle is 2.5 MM higher than stock. I was amazed at how much better the bike runs at this setting. It is anly .032" higher than the last setting but no more lean surge and the engine pulls cleanly at any throttle setting in any gear. Basically what has been done is to take the 2.5MM spacer off the top of the needle and run 135 jets. If you have a GS700 and want to run POD's this would be a good place to start.

 

[LeeGS550E]

Glad to hear that you got it figured out. I am ditching the EMGO's on my 700 and trying out some Uni's...good to know that my jetting is right in the same range as yours. I am going to adjust my needles as you have, though, because I'm still having problems in my transition area. Thanks for the follow up post!

 

[KEITH KRAUSE]

OK here is what I found out. Contrery to what the previous owner told me the main jets were 135's instead of the stock 122.5's which would account for the top end running good. I pulled the last of the washers off of the needle which now means the needle is 2.5 MM higher than stock. I was amazed at how much better the bike runs at this setting. It is anly .032" higher than the last setting but no more lean surge and the engine pulls cleanly at any throttle setting in any gear. Basically what has been done is to take the 2.5MM spacer off the top of the needle and run 135 jets. If you have a GS700 and want to run POD's this would be a good place to start.

Glad it's running better. As per my first reply, I'm not surprised it runs well on the 135's. Obviously the needle still had enough adjustment to fix you up too.
I would still test and see the plugs at full and 1/3 throttle. A bike may SEEM to run well but you'll be amazed at how well it runs once the plug colors are acceptable.
You may have it right but I would not assume based on "seat of the pants". Test.