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Need help from the carb jetting gurus ...

Steve

Steve

GS Whisperer
Working on a set of carbs for an '80 850.
Owner says he has pods and a stock pipe.
Stock main jets are 115. Should I install 120 or 122.5?
These will be mailed back cross-country, so I won't have the opportunity to fine-tune the jetting. :o

.
 
K&N pods?
I'd start with 125s. You'll also need to raise the needle about three washers (1.5 notches) and drill the slides for the pods.
Couldn't talk them into a jet kit? :)
 
With just pods and a stock pipe I did not think a kit was necessary.

I know with my son's bike, which has stock airbox and a header, 120 mains are working quite well.
I did not think that pods (only) would flow that much more. :o

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Steve said:
With just pods and a stock pipe I did not think a kit was necessary.

I did not think that pods (only) would flow that much more. :o

.
Click to expand...

Biggest hole in the system... it would also make sense that pods and a good pipe wake these LEAN and not so mean engines up and run like a whole new bike. ;)
 
Leave the Main jet alone. (!!!!) trying to keep the emphasis to myself-

bump the pilot jet larger and might need to shim the needle. ride it to see

most street riding happens on the pilot circuit including the transfer holes- and needle jet-

main jet tuning is for WOT above 6000 rpm. are you really riding in that range?? no
 
trippivot said:
bump the pilot jet larger and might need to shim the needle. ride it to see
Click to expand...
Well, I'd really like to be able to do that, the ride part, that is, but these carbs were mailed to me for cleaning and rebuilding.

I have no problem putting different pilot jets in, but that raises a question:
A "jet kit" (usually DynoJet) seems to be the cure-all for quick jetting fixes on this forum. They do not usually include different pilot jets, yet you suggest that is all that might be necessary besides shimming the needle. How do all these "kit" users get by with that?

Also, "riding it to see" is out of the question. As mentioned, these were mailed to me and will be mailed back. Also, I will not be close enough to the bike after they are installed to be able to do any of the fine-tuning, so I want to get it close to start with.



trippivot said:
... most street riding happens on the pilot circuit including the transfer holes- and needle jet-

main jet tuning is for WOT above 6000 rpm. are you really riding in that range?? no
Click to expand...
I have no idea how the owner of this bike will be riding it. Yes, most riding happens on the pilot and needle circuits, but running lean on the mains is where damage will show up the most dramatically. :eek:

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Dave8338 said:
Biggest hole in the system... it would also make sense that pods and a good pipe wake these LEAN and not so mean engines up and run like a whole new bike. ;)
Click to expand...
I have never had the pleasure of a before-and-after comparison with pods and/or pipe conversions, so I don't know how much they "wake up". But, as noted in the original post, this bike has pods and stock pipe, so I wasn't sure how much would be necessary.

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You should be able to richen the pilot circuit using the mixture screw alone.

I'd go along with Chef1366's suggestions on the other changes, maybe even higher on the mains as moving to pods make so much more difference than changing the pipes.

A bit hit and miss doing it 'by post' but it'll be miles better than running as it is. Dynojet might be the easy solution but I would never use one myself (never had too and don't see any reason to change) so I'm not qualified to comment.
 
I know a guy who ..

Steve said:
I have never had the pleasure of a before-and-after comparison with pods and/or pipe conversions, so I don't know how much they "wake up". But, as noted in the original post, this bike has pods and stock pipe, so I wasn't sure how much would be necessary.

.
Click to expand...
 
air box on= tinker with carbs for improvement.
air box off= must have st.3 jet kit to be correct(the needles is the magic/cant shim fat blunt shock needles enough to help).
when installing a jet kit the idle circut must be 100% stock as far as the jets are concerned.
this information is for suzuki GS vaccum carbs..
the exhaust doesnt matter, the air box is the deciding factor here.
steve,
got your P/M.
see if tck or whoever else may want to also get togather sometime.
waffle house/frishes doesnt matter to me.
 
I bump the pilot jet up with a pipe and pods. Keeps the idle mixture screws from coming out 5 or more turns out. Vance and Hines old school suggestions with their pipe was to remove the airbox lid and bump up the pilot jet one step.
 
Just my opinion but this is not going to work via post as firstly every bike is different, secondly stock pipes dont work well with pods in my experiance & thirdly you need to be there to fine tune the thing if by any small chance it does run

I may be wrong here but the comment above about not being on mains untill 6000 revs seems incorrect imo it should be coming on to the mains somewhere around the 4000 revs mark

last thing even on very highly tuned bikes ive never had to change the pilot jets so i'm not sure what thats all about

cheers tone
 
I'm right with Tone on the pilot jets - I've never had to change any and that includes pods, bellmouths etc. You can even get a decent tickover / first 1/8 throttle with nothing at all stuck to the inlet side of the carbs just by playing with the mixture screw.

However, the revs thing is a bit misleading - the key is the amount of right hand twist i.e. it's all about throttle opening.

I'd also agree with Tone that pods and stock pipes don't go well together usually. I'd go one step further in fact - unless you're right on the numbers pods don't go well with anything. 9 times out of 10 a motor fitted with pods is running worse than a stocker.
 
I feel the urge to post so here it goes, http://www.dynojet.com/pdf/3315.pdf

Is a great resource, use that as a baseline. Always remember Mikuni and Dynojet are different.

My bike is an '81 750L so there is a lot of differences but will offer my opinion.

Keep the pilot jets stock! Go bigger on the mains, and drill the slides like it is noted. The air modifiers are big in the proper tuning of the low end fuel delivery.

Your not going to nail these carbs in one shot, but I would recomend the purchase of a DJ kit. I can say that I had pods on before I changed my pipe, and it can be tuned! After I put my V&H on it was as simple as adjusting the clips on the needles to get the bike to optimum performance!

If this helped great if not sorry to chew up the bandwith!
 
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