One for the Gurus

[77crewcab]

Been working on the carbs trying to get it running better and keep finding the same problem with each change. When starting cold with the choke on the bike will stumble and run rough at 1-1300 rpm. But as it warms up the idle will smooth out some and then the rpm starts to rise steady to about 1500 and once it hits 1500 will gain rpm as though doing a smooth steady but quick roll on of throttle. It will continue to rise to over 4K which is when I hit the kill switch. It does the even if the throttle cable is disconnected. It will not do it every time but more like 7 out of 10 times. When it doesn't rise on its own I can blip or roll on throttle either one and it will hang up and not idle down. Sometimes it will float down back to idle and sometimes will stay at 25-3000. All of this is with the choke on or off, however it is very difficult to get it to stay running if the choke is off and I am not working the throttle. It feels like I need to turn up the idle speed for when the choke is off, but yet at the same time the rpms seem to act on their own.

Does anyone know what is going on or where I should start looking? Except for an intermitent backfire which seems related to bad plug caps (will follow cap reguardless of cylinder, more ordered and will be here Tues) the engine seems to be running well. I have done the bread tie sync, supposed to have a merc sync tool on the way but haven't gotten it yet.

[red bandit]

vacumm leak or carbs need cleaning. Spray carb cleaner on carb boots and throttle shaft on carbs while engine is running around 1100 rpm, slow idle screw to get it at 1100, might have to touch throttle a little to keep it running. If a leak...rpm will change. If no vaccum leak..carbs need cleaning. Disassemble carbs spray all the passages with carb cleaner..let carb sit for 5-10 min...spray again...repeat...repeat...repeat. blow out with air. If it still revs high...repeat above.

[mro]

Vac sync carbs?????

"bread tie" bench sync can get em close, but still need to use gauge or mercury sticks.

One carb outa sync can run the RPM's up as you describe.
___________



mro

[77crewcab]

Carbs have already been cleaned several times, no vacuum leaks external of carbs. New vac hose for advance, fuel octopus removed, all vac nipple on carb boots plugged, outside of carb boots coated in rtv to seal up any leaks that may have gotten through the cracks (though none were visible on the inside of the boots) I am leaning towards the carbs out of sync or and internal vac leakage of some sort. Any other thoughts?

[mro]

Any other thoughts?

YUP!!

but this is a PG forum


mro

[77crewcab]

Well I am definately leaning towards carbs out of sync. Went and fiddled with it some more and seem to have stopped the uncontrolled rise in rpm. Still have a problem with the revs not coming down very quick after revving the engine. The throttle cable is ruled out as it is disconnected. I guess I can either try to tune by ear, get the merc stick from a friend 7hrs away (anyone know if it illegal to mail these cause of the merc), or try and build the vac sync tool in the tech tips.

[John]

Hazardous goods

That's a good question. I wouldn't think mercury could be shipped by mail, or package delivery company, but how did you recieve them? UPS? USPS? Fedex? They must have been shipped to your address, so check with those companies, and see if you can have them sent legally. Maybe the mercury has to be in some special shipping container?

[77crewcab]

I haven't received them yet. My friend bought the carb stick at a local shop in Austin and was going to give it to me since he sold his bike. I said at first to just mail it to me not even thinking about it. But he said USPS couldn't ship it.

[TopCatGr58]

Hey Crew,

If you have a Harbor Freight store near by, they have a vacuum gauges for less than $10.00, and you can make your own with a foot or so of PVC pipe, a couple of fittings, etc.. You can get fancy with an aquarium rack of valves, but mine didn't want to work so I just put the hose on each carb, and synched them that way, took a while but got it done. No worries about Merc. either!
T.C.

[HobbyMan]

FInd an excuse to go see an old friend. 7hrs isn't that far. There must be some ground shipment that you can ship HC. I realy don't think that they care. Besides, If the carb sticks have never been used, the mercury should be sealed up in its own container.

[77crewcab]

Looking over Fedex site looks like they will ship hazmat next day air so I will look into it. Until then I may look at doing the the single vac guage and pvc pipe I think al I would need is the pvc and hose barbs, already have a vac guage.

[77crewcab]

Read the tech tip several times and it doesn't seem to say what size or length of pvc pipe to use. Can any one shed some light?

[mro]

Does not have to be much, 1 1/4 or 1 1/2 by 8/10 inches long.

I just used a plastic vacuum cleaner attachment , duck taped the ends , barrowed the vac gauge of the brake bleeder and the hose from a petcock. Had the right size hose barb

Not that I'm cheep, just XSive



mro
btw, after you put it together, place small bolt on hose with a hose clamp. Attach to carb boot with engine running. Tighten hose clamp over bolt till the vac needle stops pulsing.

[77crewcab]

I used 2" x 12" with caps on each end sealed with rtv and ductape and found that a c-clamp works well as a control device rather than an aquarium valve or hose clamp.

[77crewcab]

BTW I know that all carbs are supposed to be equal and that is the most important thing, but is there a specific range to shoot for?