carb pointer

[ap72]

I just "re-jetted" my carburator with a drill press and a screw driver. No its not scientific, and unless you have expierence doing it that way (I've done MANY car carburators) I would not recomend it unless you have a lot of time and extra jets.

HOWEVER one point I would like to suggest that I think many overlook is float level adjustment. I noticed many people are having problems with their carbs and are only swapping out jets. While that is a good start I find that altering the float level is how you can really tune that particular jetting. Higher fuel level means more fuel (just as a reminder). I retuned my carbs in a day and only had to take them off about a dozen times.

ALSO when tuning I recomend finding a small container to use as a fuel cell and only run it with about a pint of fuel. Its easier than having to keep hooking up the tank and pulling it off, and it still does a very nice job.

 

[first timer]

some points raise here are good but i would be carefull with raising float levels, i would keep them at factory speced levels unless noted by a specific set of instructions that come with tried and test carb kit. it is also not a good idea to just drill out your main jets as to rejet carbs, these things are all carfully measured and tested. Rember there are at least 3 diffrent fuels metering circuts in carbs so adjusting one will only fix one range of rpms, leaving the rest to operate poorly.

just a suggestion if you must rejet you carbs for what ever reason then please get a jet kit it will be well worth the price vs the the time it will takes you to shade tree somthing.

-ryan

 

[ap72]

I disagree with the need for a "jet kit" While I do agree that you should normally buy jets at pre drilled sizes the "kit" will not be a perfect match, but just a good patch. I would highly recomend using a A/F meter though and going from there. those things have been invaluable in my tuning, and while they are kinda pricey you can reuse it over and over again, and splitting the cost with a buddy can also help.

 

[KEITH KRAUSE]

Float levels are important but you need to stay within any factory range of adjustment.
And as first timer said, there's more to jetting than just the main jet. The main only regulates at 3/4 to full throttle. The pilot jets, if you modified them, only regulate closed throttle to about 1/5 throttle position. In your case, you still have haven't re-jetted the jet needle which is the most important circuit to get right.
I have no problem with jet kits. I've installed a lot of them. Some also supply pilot air jets which need changing. Lighter springs for the CV carbs and vacuum port drilling instructions. Float bowl vent line removal (how many would know this is necessary when running pods?) There's more to jetting than many think.

 

[RacingJake]

You better get out while you can Keith. Big Bear, Lake Arrowhead, Crestline then you.

Run Man Run

 

[ap72]

actually the main jet meters a lot more than just 3/4 to full throttle- which is a mistaken assumption that will make trying to tune these things a huge PITA. And as for the needles- I even modified those and the springs for the diaphram assembly.

The great thing about these bikes is that IF YOU KNOW WHAT YOU'RE DOING then there is a lot of tuning/power gains that can be made with very little expense other than time and a few basic tools.

One thing I would like to see is if anyone has made any noticeable power gains by porting/polishing the head and port matching the intake and exhaust while using the stock cam. I don't want to give up any low end torque and would like to know if these typically high hp modifications help some down low too (as they do on a typical V8). I'm thinking about doing these when I rebuild the engine along with getting some milled off to raise compression a bit. I'm not going for a high rpm screamer, but rather a perfectly tuned cruiser.

 

[Deesel]

[/I have no problem with jet kits. I've installed a lot of them.QUOTE]

Keith Krause you must not be doing it right if you havent had any problems!LOL- just kidding.
Keith repeatedly gives excellent precise and accurate advice on carburator tuning. Heed his advice. You will benefit.

 

[ap72]

please dn't take what I'm saying to mean jet kits don't work. They do work, and they can work for a lot of different setups. The thing is that they will not be the best tune for any of these setups. they'll be way better than stock for sure but you still may have an MPG or a HP pr a FTLB left on the table unless you really tweak it all just right. And then do it again in a month when the temp and the humidity changes.

I'm hot saying the kits are bad, and I'll even go so far as to say they're great for novices- but they're not the end all.

 

[Deesel]

[The thing is that they will not be the best tune for any of these setups./QUOTE]
Those kits are designed for specific applications.
I extensively modified my airbox and figured it would flow close to what k&n pods would.
I had a V&H pipe and figured a Dynojet stage 3 kit would be close- it wasnt. So rich it would hardly run. If the kit says to use K&N pods and a quality performance exhaust- the kit is not calibrated any setup in between.
There is a big difference in jetting on these GSs when going from the stock airbox to modded airbox, cheapo pods, K&N pods or velocity stacks.
Your right, there are many factors that affect carb tuning- temperature, altitude, air density, engine setup, etc.
I was just joking with Keith Krause because he is passionate about helping people with carburation issues and offers excellent knowledgable input to anyone.
This website provides a wealth of information that might normally cost a person alot of time and/or money.

 

[ap72]

I'll agree with this place having a lot of info- sometimes not easily understood, but its almost all there.

 

[KEITH KRAUSE]

I just pass on experiences that have worked or not worked for me.
I try to give advice when I know what I'm talking about. I certainly don't know all there is to know about carbs but if there's a subject I'm not sure about, I always tell the person asking for help. If still interested in my advice, I suggest something and maybe we all learn something.
Jet kits don't always work perfectly for all bikes. Too many variables. If your bike is equipped differently or your mods go beyond the intended range of the kit, then you can't expect good results. I think most people have problems because they use cheap filters and cheap pipes or have mods that don't match well. Many more people have problems because they don't prepare the bike for the re-jet. They don't clean the carbs right, adjust the floats right, they re-use old o-rings, don't check the electrical system, timing, valve clearances, cam timing.....then they blame the jetting if they get poor results.
I try to let people know you have to do certain things to get good results.
I could also go on about jetting circuits and at what specific throttle position they regulate but if someone doesn't believe me, then do it your way. But I don't like to know that others are reading these threads and getting incorrect info. In that case I have to say something.

 

[abates226]

Hey Keith...what's this about no bowl vent lines on podded carbs? Mine was already podded up and rejetted when i got it ('80gs1000s) and had the stock exhaust on it. Started up good, although seemed a little cold blooded. Now I've put v&h 4-1 on it and disassembled carbs completely for cleaning, reassembled everything and sync'ed carbs. Had one heck of a time getting the thing started the first time. I figured ok, hasn't run in months, not enough fuel in the carbs yet, blah, blah, blah. After running for a while, backfiring the whole time on decelleration of the engine, one pipe appears to be running a whole lot colder than the rest. Never noticed it before, but then the old pipes were black, so I wouldn't have seen the discoloration difference. After 4 or 5 hours sitting the thing is once again harder than heck to start. Like running the battery all the way down and then having to push the bastard! Any suggestions? Haven't checked plugs, wires, timing, coils, nothing. Does anything obvious jump out at you? Bowl vent tees are still in place...didn't know about killing those with the pods...what's that about? Thanks

 

[KEITH KRAUSE]

Hey Keith...what's this about no bowl vent lines on podded carbs? Mine was already podded up and rejetted when i got it ('80gs1000s) and had the stock exhaust on it. Started up good, although seemed a little cold blooded. Now I've put v&h 4-1 on it and disassembled carbs completely for cleaning, reassembled everything and sync'ed carbs. Had one heck of a time getting the thing started the first time. After running for a while, backfiring the whole time on decelleration of the engine, one pipe appears to be running a whole lot colder than the rest. Never noticed it before, but then the old pipes were black, so I wouldn't have seen the discoloration difference. After 4 or 5 hours sitting the thing is once again harder than heck to start. Any suggestions? Haven't checked plugs, wires, timing, coils, nothing. Does anything obvious jump out at you? Bowl vent tees are still in place...didn't know about killing those with the pods...what's that about? Thanks

If the bike was correctly jetted for the pods, you'll have to re-jet for the pipe addition.
Jet kits require you to remove any float bowl vent lines when running pods, to avoid fuel starvation from inadequate bowl venting. Leave the vent ports open.
You're probably lean on the pilot jet circuit too. Be sure the carbs and all the very small pilot circuit passages are clean before re-jetting. That, and possibly a poor bench synch, would make the bike very hard to start in preparation for the vacuum synch. If it's synched correctly now, the lean pilot circuit will still be trouble.
One pipe running colder than the other and how it relates to color? Not sure what you're saying. If you have one cylinder blueing up the pipe, then that cylinder is hotter/leaner than the others. If one pipe isn't turning blue and the others are, and it's actually cold/colder to the touch, then I suspect a weak spark at that cylinder. One weak sparking cylinder will cause trouble as you know also. Could be a poor connection at the plug cap, coil, cracked/arcing lead, etc. A weak coil should effect two cylinders, either 1/4 or 2/3.
Checking the electrical system and timing/advancer action is part of basic tuning before attempting a re-jet. All four cylinders must be firing correctly before doing a vacuum synch.
A new pipe should always get new gaskets too. Exhaust leaks will contribute to decel' popping, even with perfect jetting.
You'll also have to take reads to see what the jet needles (1/3 to 1/2 throttle) and main jets (full throttle) are doing. But not before basic tuning and a good vacuum synch and the mixture screws are set for best idle.

 

[trippivot]

jet kit or not??

jet kit or not??

street bikes run on the pilot circut and needle circut over 80% of the time

the needle taper is probably the most important detail you need when buying a jet kit to get a rideable machine after putting a pipe on the bike,especially if you remove the air box too.

changing only the main jet will help with wide open throttle over 6000 rpm's
if you shim the stock needle that is not enough.
raising the fuel level is not a tuning detail

make as many excuses as you like, the dyno jet kit is by far more researched and sucessful than a back yard untuner

spend the money and do it right is what I say