kliff....... fuel problems

[jct842]

I have been having starvation problems intermittently at wot. scoot cuts out and backing down the throttle for15/20 seconds gets it going again. I was going to log some speed verses rpms today and went back home and put a fuel pressure gauge on. in subsiquent runs it never got quite to cut out though was starting to act up. the gauge went from a normal 2 lbs down to less than 1 almost to zero. I then went home and hooked it to the vacuume line. under wide open it went down to almost zero and engine again did not completely cut out. just barily an indication on the gauge, probably 1hg of vacuume where it was around 15 at idle. I would prefer having a vacuum fuel pump, do you think if I were to buy one of them super hd vacuum pumps they sell in the $40 price bracket I could get by? An electric is always an option too but would prefer the other.
John

[harrywr2]

I'd buy 3/16" Goodyear/Gates SAE J30/R7 vacuum hose and 1/4" brass fittings first. It'll fit tighter then a nuns no-no. But that's what you want on vacuum lines.

[Rebel]

I agree, first upgrade the hoses and if that does not take care of the problem consider a new pump. Include some good fuel lines too.

[kliff]

Aug 21, 2009 22:41:58 GMT -5 @jct842 said:

I have been having starvation problems intermittently at wot. scoot cuts out and backing down the throttle for15/20 seconds gets it going again. I was going to log some speed verses rpms today and went back home and put a fuel pressure gauge on. in subsiquent runs it never got quite to cut out though was starting to act up. the gauge went from a normal 2 lbs down to less than 1 almost to zero. I then went home and hooked it to the vacuume line. under wide open it went down to almost zero and engine again did not completely cut out. just barily an indication on the gauge, probably 1hg of vacuume where it was around 15 at idle. I would prefer having a vacuum fuel pump, do you think if I were to buy one of them super hd vacuum pumps they sell in the $40 price bracket I could get by? An electric is always an option too but would prefer the other.
John

I ran this kind of Mikuni Vacuum pump on Kart racing, for years, using alcohol, where fuel suppy and demand was MUCH higer than with out GY6 engines. 10 laps, on a 3/4 mile track, 1.5 gallons of fuel sed....you do the mileage! cgi.ebay.com/ebaymotors/Mikuni-Type-Single-Fuel-Pump-popular-4-snowmobiles_W0QQcmdZViewItemQQ_trksidZp3286Q2ec0Q2em14QQhashZitem2ea7311939QQitemZ200373508409QQptZSnowmobileQ5fPartsQ5fAccessories

Another trick we did, was hook up the vacume line to the valve cover breather on the engine. Suction/vacuume, never seemed to vary the, not even at WOT. Still ran a breather box, vented about a foot or so from the engine, but had the punp vacume line as close to the CC breather, or valve cover as possible.
No more WOT lean runs, fuel from idle to wot. Give it a shot, faily cheap even today.

[jct842]

Thanks every one.....will look into crank case venting and I have ordered the mikuni pump. I just dont like the idea of an electric pump. too many if's when you have fuel pressure and the engine isn't running. only as a last resort.

[jpn]

How much vaccuum is normal at full throttle? While trying to sort out an assortment of problems on a couple of engines, yesterday, I was reminded that the manifold pressure gauge shows a green arc that includes a vaccuum of about 1/2 inch of mercury (around a quarter psi). This was on fuel injected engines, so they don't have a venturi. It's probably been years since I worked on a carbureted engine that had a manifold pressure gauge installed, so I can't recall the upper limit of the green arc on their gauge.

[jct842]

wow.........I am a happy camper. for the first time i ran full throttle and it did not run out of gas. now on to finish tuning jets and rollers. It is my recomendation that when some one buys the hoses and other things for the pdi on the new scooter that he invest $25 or so for the mikuni fuel pump. on my vacuum gauge I have 12/10 at idle and about 1 inch at wot. I am running too rich as my briggs and stratton muffle has a coating of soot inside it. ! john

THANKS GUYS, YOU HAVE MADE MY LIFE BEARABLE!

[Rebel]

Sounds like you did the work to me, glad you like the way it goes now.