jetting database/support group?

[Anonymous]

i am having the oddly familiar problem it seems everyone else is having. i have an 80 gs100e with cv carbs, 4-1 pipes, individual pods i'm trying to stage 3 jet and i keep trying to figure out if i'm a total idiot. the dynojet troubleshooter seems to be little help. is it just a matter of experience?

i was wondering if this would be a good forum to simply invite anyone interested to list jetting setups they have actually gotten to work. i think it woud be a nice way to direct folks (myself included) to a proven setup that will hopefully need minimal tweaking for a given application instead of the alchemy that jetting appears to be.

thanks,
Scott

 

[KEITH KRAUSE]

Yes, it would be nice to find other people that have the same mod's and have jetted correctly. However, to just simply copy the jetting someone else has done and be 100% sure of the results, you would have to have identical mod's, identical engine condition, similar elevation/climate, and trust the person you are copying from.
Just a differently shaped pipe could make the copied jetting not work for you. Jetting can be a lot of trial and error. The more you do it, the better you get. It takes time and patience, and you have to be careful when working on carbs. You need to keep notes and test. You feel how the bike performs and take lots of plug reads. It's not just about jetting. You also need good compression, valves adjusted correctly, correct ignition timing and a strong spark, etc. So there are a lot of variables.
I have a '79 1000, but it has the infamous VM26mm carbs. It was a lot of trouble, but it runs great. I've heard if you can get my carbs jetted right, you can get any carbs right.
So you have a 4-1 pipe, what style/brand?
Pod's, what brand?
Dyno-jet kit, good choice.
What condition is the engine in? Good compression? Ignition timed right, good spark? Whats your elevation?
Tell us what is going on. How does the jetting feel right now? What color are your plugs? Remember, the Dyno-jet "base settings" are just a starting point. I've never had a bike or helped someone else, who was happy with the base settings. Did you remove the 2 floatbowl vent tubes?
We can get it running good, but you may have to change the needles a few times, etc. If you're able to do the carb work, I'm sure we can help.

 

[Anonymous]

thanks for your help. the pipe is a vance&Hines off an 1100- i just had to cut down the megaphone to mount it, the pipe is unmolested. the pods are emgo.

i installed the dynojet kit including drilling out the slides-effectively scaring the crap out of me- to their suggested base settings: from stock 112.5 to 175 mains-seemed a little rich to me, needle clips to the second position, synched the carbs and began tuning. i got some positive results moving the needles up thereby richening the mixture but i'm still popping out the carbs (lean) and foulfing plugs (rich) while the bike refuses to cruise- at steady rpm it stumbles and backfires, however wot and accelerating in general is not bad which lead me to beleive the mains are ok. idle quality is about like cruising.

the bike itslelf is in great shape, low miles good compression and ran like a champ before i decided to mothball the airbox and stock exhaust.

i'm in bloomington, IN-about 700 feet above sea level

i did pull the float bowl vent tubes. and i'm awfully concerned i trashed the slides when drilling them.

thanks again,
Scott

 

[KEITH KRAUSE]

Hi. I have the older VM carbs, so I never had to modify the slides. If you did mess them up you'll never get it running right. The vacuum and draw of mixture will be compromised.
You say the bike was running good before the mod's, so I assume the carbs are clean, float heights good, diaphragms and other rubber or moving parts are good, diaphragms seated properly, floatbowl vent tube nipples clean/clear, filters properly oiled, ignition timed right/good blue spark.
That does sound like a big increase for the mains, did Dynojet give you more than 1 size to try?
Popping out the carbs, do you mean while idling/start up or while closing the throttle after accelerating? It's not always possible to eliminate this without causing another problem. Dynojet does warn us about some "driveability" problems. If the popping is not too bad, you may have to live with it. I believe your carbs have a pilot/mixture screw, have you tried adjusting it? Turning it out will increase the amount of fuel mixture.
It sounds like your biggest problem is the plug fouling and steady speed problems. The pilot circuit has an overlap effect on the needle circuit at speeds of about 65 mph and below in top gear. The main does not have effect until about 3/4 throttle. You started with the needle clip in #2 groove from the top. Where is it now? Groove #4 seems to be a common position for your model, or at least "ballpark". Sometimes using the spacer for 1/2 groove adjustments helps. A good carb synch' is very important.
I'm not real familiar with your kind of carbs, but if you did damage the slide(s) (pistons, correct?) you will have to replace them. Let us know how things go.

 

[Anonymous]

The shorter megaphone is something that will throw the jetting a bit off tt diferent rpms. My secret to success(( :lol: :lol: :lol: whenever i am lucky enough to have success)) is to do one mod at a time. This is often quicker than changing 3 items and taking weeks of aggrivation to sort out the tuning.

 

[daveo]

was there a stock spacer on the stock needles? Did you use the stock spacer on the Dynojet needles? I remember having a similar issue that was cured by re-installing the stock spacer on the Dynojet needles, can't remember for sure which groove I clipped, I think it was the middle one though

 

[Anonymous]

hey thanks for all the help. the needles are currently on clip 3, and it sounds like i should work the pilot circuit. i will also try using the leaner 165 main that came with the kit.

the backfiring is most prominent at low and mid-throttle acceleration-does go away when i give it the spurs and the afterfire of course on decel-like you said a certain amount of that is unavoidable.

daveo-i did use the exact spacer setup that was there to begin with as outlined by the dynojet instructions.

slopoke- i agree i should probably try and keep it one at a time but the i've already drilled the slides.

one bit of info i came across is that the slide holes are originally macined at an angle and that the same angle should be maintained while drilling them out. this info would have been nice to see on the instructions. if anyone has untouched cv carbs i would be very interested to know if the holes are in fact at an angle. if so, does anyone know where to buy new slides.

i'll keep progress reports coming

Scott

 

[daveo]

.

one bit of info i came across is that the slide holes are originally macined at an angle and that the same angle should be maintained while drilling them out. this info would have been nice to see on the instructions. if anyone has untouched cv carbs i would be very interested to know if the holes are in fact at an angle. if so, does anyone know where to buy new slides.

i'll keep progress reports coming

Scott

Yes, they are drilled at an angle, not sure that that would be the problem though

 

[KEITH KRAUSE]

Hi. As I said before, I'm not an expert at CV carbs, just want to learn more about them, so take my advice with that in mind.
What is the purpose of drilling out the slides, to improve throttle response?
The increased vacuum lifts the slide up faster? If so, this would effect velocity and the vacuum and the amount of fuel being drawn up into the cylinder. If there was something wrong here, it would be the most noticable at low to mid- throttle opening. I'm not sure, but if you changed the angle of the hole in the slide you may never be able to re-jet. The vacuum and flow of mixture may be compromised. You need to call Dynojet on this, they were very helpful when I had questions.
If the slides are OK, I'll move on.
What color are all 4 plugs ? Without this info, we have to rely on words like backfiring, surging, sputtering, etc, that can be interpreted wrong.
You say it's backfiring at low/mid throttle and clears itself as the throttle fully opens. This would be mostly the needle circuit, with a smaller overlap effect from the pilot circuit. Backfiring, to me, is usually associated with too much fuel in the mixture or incorrect ignition timing. You say the backfiring got a little better when you raised the needle 1 position. This would richen the mixture and increase the chance for backfiring, so I'm not sure I understand. Having your clip in groove #3 does not seem too rich. I have read posts by members here that say groove #4 gave them good results. They had similar mod's.
Is your ignition advancer working properly? This could give you the problem you describe. Is the timing correct? Carbs SYNCH'D ?
As for the pilot circuit, I would try adjusting the pilot screw out some before increasing the pilot jet size. On many Dynojet kits, they say the pilot jet MUST remain stock for their jetting instructions to work. Again, call them. If they say your slides are bad, there's no point trying to jet.
Talk to you later.

 

[daveo]

my experience with carburetor induced backfiring is that, if it's backfiring out the intake, you're lean, backfiring out the exhaust, you're rich,

 

[Anonymous]

my experience with carburetor induced backfiring is that, if it's backfiring out the intake, you're lean, backfiring out the exhaust, you're rich,

Thats the first time i have ever seen it told properly. Most folks say that backfiring just means lean.
Except for mexican food.