carb work recommendations

[rideOn]

i'm in sc and the temps have gone from 80/90 to 60/70. my 850 wants to stutter between 3-4k rpms. these are my thoughts and i welcome suggestions.

next paycheck i am replacing o-rings, intake boots (with new clamps) and new air filter (original). the previous owner put on a 4 to 1 exhaust, but i have no dough to fix that now. he also put (rumor has it) bigger jets and i don't know the size. i'm thinking factory jets to benchmark, and then go from there. i also plan to re-wrap the baffle.

oh, and shims for the valves.

thoughts?

[Steve]

Well, since you KNOW it already has a different exhaust and it will HAVE to be re-jetted, there is absolutely NO sense in putting stock in there "for a baseline". My son's bike has a header and stock airbox (K&N filter inset), so it's a bit like yours (click on "#2 son" link in my sig). I have 120 main jets in there and it seems to be working rather well. I have not taken the time yet to do proper plug chops to verify jetting, but it starts easily, warms up quickly and pulls well at any engine speed, so it's at least close.

First thing to do is to get your carbs apart and actually see what's in there, then we can do some more-intelligent guessing.

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[rideOn]

First thing to do is to get your carbs apart and actually see what's in there, then we can do some more-intelligent guessing.

.

nothing like a good edgamacated guess!

[jabberjoe87]

i agree that 120's are a good baseline, i have a 4-1 and pods on my 750 with 120's so with your bigger displacment you should start there and order some 122.5's along with it incase you needa go bigger

[rideOn]

i don't know what's in it now. they're cheap enough to swap all of them out

[twr1776]

Today, 01:18 PM Steve Well, since you KNOW it already has a different exhaust and it will HAVE to be re-jetted, there is absolutely NO sense in putting stock in there "for a baseline". My son's bike has a header and stock airbox (K&N filter inset), so it's a bit like yours (click on "#2 son" link in my sig). I have 120 main jets in there and it seems to be working rather well. I have not taken the time yet to do proper plug chops to verify jetting, but it starts easily, warms up quickly and pulls well at any engine speed, so it's at least close.

First thing to do is to get your carbs apart and actually see what's in there, then we can do some more-intelligent guessing.

I agree with Steve on upping the mains two sizes for the pipe and would also suggest bumping your pilot one size if you are still running the stock airbox. I have a similar set up on my 1000 and my plugs read slightly rich, no decell popping, close enough for me. Slightly richer is always better than leaner IMHO.

[Steve]

i don't know what's in it now. they're cheap enough to swap all of them out

OK, before you go taking everything apart, put some new spark plugs in and do some plug chops. Don't know how? Look at BassCliff's site, there are instructions there on how to do that.

Now, before you go ordering parts, let's say that you order up some 120s and 122.5s. While you are waiting, you do your plug chops and find that the mixture is close, but just a tad lean. You open your carbs and find 125s. You just wasted money on TWO sets of jets.

First things first. Follow Nessism's advice: "To measure is to know."
1. Check the mixture with new plugs.
2. Open the carbs to see what's in there
3. Adjust accordingly.

And, if you find that urge to get rid of some money just overwhelming, let me know, I'll PM you my address.


.

[rideOn]

I have a similar set up on my 1000 and my plugs read slightly rich, no decell popping, close enough for me. Slightly richer is always better than leaner IMHO.

yep, i'm getting me some decel popping. she cranks very fast and idles well, so i never thought about pilots. the big problem going on is the 'flutter' between 3-4k rpms. above and below that range, everything seems ok. i don't see a height adjustment for the main needle, so bigger mains make sense. i'll get those valves and new boots done first and go from there. ??

[Steve]

Don't guess, EXAMINE.

Do the plug chops, make adjustments as necessary.

.

[rideOn]

i wil do the chops this weekend. do i just need one set of fresh plugs or a new set for each rpm range? if only one set is needed, do i need to carry along a brush to clean the plug between chops?

[tkent02]

i wil do the chops this weekend. do i just need one set of fresh plugs or a new set for each rpm range? if only one set is needed, do i need to carry along a brush to clean the plug between chops?

Use your old plugs, what changes color is the deposits on the plugs, with new ones there's little to see unless it is very rich. You don't need to clean the plugs.

[rideOn]

less money, mo better. i'll report back here when i get some readings and maybe everyone can hepp me interpret.

[twr1776]

Yesterday, 02:42 PM rideOn yep, i'm getting me some decel popping. she cranks very fast and idles well, so i never thought about pilots. the big problem going on is the 'flutter' between 3-4k rpms. above and below that range, everything seems ok. i don't see a height adjustment for the main needle, so bigger mains make sense. i'll get those valves and new boots done first and go from there. ??

Checking your valves and replacing the intake boots and o-rings is definately the way to go before you even start on checking the jetting. Have you checked and/or sealed the airbox? Also check the airbox to carb boots and make sure they are still OK. The stock needles do not have the adjustment notches in them but do a search on shimming needles and you will find out how to do it with the stock needles. I shimmed mine with the Radio Shack washers (2 I think), and went 1 1/2 turns out on the pilots. The plug chops are the best way to see exactly what you have on the mix for each circuit once you have done the necessary valve adjustment/boots/etc. I am not a carb expert but that is what worked for my 1000.

[rideOn]

Checking your valves and replacing the intake boots and o-rings is definately the way to go before you even start on checking the jetting. Have you checked and/or sealed the airbox? Also check the airbox to carb boots and make sure they are still OK. The stock needles do not have the adjustment notches in them but do a search on shimming needles and you will find out how to do it with the stock needles. I shimmed mine with the Radio Shack washers (2 I think), and went 1 1/2 turns out on the pilots. The plug chops are the best way to see exactly what you have on the mix for each circuit once you have done the necessary valve adjustment/boots/etc. I am not a carb expert but that is what worked for my 1000.

i wanted to head for getting everything good and tight first...good advice. that's on the list 3 weeks out (when i get some dough). my single has a carb with a needle height adjustment for mid-range, but i couldn't find anything in the forum links or my manual for the gs. for now, when i'm in that 3-4k range, i push the choke over about 1/3 and it smooths out nicely.

[twr1776]

Here is a link on needle shimming from BassCliffs website.

http://members.dslextreme.com/users/bikecliff/images/carbspec_float_height.html