Fuel delivery issue on my SG

[GLoweVA]

I'm stumped and need some advice on what to look for.

On my SG it appears that after about 30 mins of moderate highway riding (65-70mph) that the left side is starving for fuel. She'll bog down and if I stop and shut her off, the bowls will fill back up and I'll be good to go.

Background:
No octy, Prime ports capped off, left side feeds left side, (vice versa for the right) I've got inline filters on each. The routing is from the petcock, down between the inlet boots then the filter as it loops around above the starter area (horizontally) and back up to the carb inlet.
No kinks in the lines and it happens whether I have a full tank or half tank, on 'reserve' or 'on'.
When it happens I can see the air in the filter, so I know it's starving for fuel.

I'm thinking of taking my petcocks out of the tank and apart to see what's up and maybe even removing the filters from the fuel lines to see if they may be the issue. (why just the left side and not the right though?)

I cleaned out the gas cap vent this spring before I did the engine swap back in and she's been running fine even up at XS East last month.
It's about a 30 mile commute to/from work (all interstate) and it happens about 25 miles in, so I don't have far to go til I get there. I've been riding her everyday for the last few months and this happens at least twice a week.

Any ideas?

[MPittma100]

Starving

May want to check the cap vent again. Look for restrictions such as kinks or pinches in the fuel line. Verify that fuel is free flowing from the petcock. Check carburetor vents for obstruction at the air filter housing.

Mike

[bikerphil]

Left side of the tank can have more junk at the bottom (sits that way on sidestand) than the right, I would try changing the filter. I'd check that side fuel tap to see if it is flowing good also. Check line for any kinks as you know.

[TADracer]

Try a simple fuel flow test.

Get yourself a 5 gal gas can, fill your tank, disconnect your lines at the carbs and put some extenders on if you need them and then open your petcocks one at a time and run about half the tank through each one into the gas can. Have a beer and watch. If both flow well then your issues will be after your fuel lines. Also, it is a good time to get a baby bottle (glass) and measure how long it takes each fuel line to fill out 6 oz.

Reason I say try this is because even at WOT these motors do not eat a high volume of fuel.

Also, routing your fuel lines so you can place a crossover line in will help balance fuel flow out .

[GLoweVA]

Good ideas all.
I've got no kinks so that's not the issue.
I doubt that it's the vent, otherwise the other side would show the same symptoms too.
I'm thinking that it may be either the petcock (i.e. clogged up) or an obstruction in the fuel line from the petcock to the filter. Either would restrict the flow to the filter.

I do like the idea of the cross connect, but that really isn't a cure, just a patch for the problem so to speak. (though it would be nice to balance out the flow to both sides of the carb bank)

I don't really have a clear baby bottle, but I think I can find something to fill up like a 32oz cup and time the left and right sides to see if there's a big difference between the two. (maybe do it with the bike on the center stand and put the 32oz back in afterwards so that the tank starts at the same level for each side tested)

[GLoweVA]

[QUOTE=TADracer;443264]

Reason I say try this is because even at WOT these motors do not eat a high volume of fuel.

QUOTE]

On the special tank (3.9 gal) and about 35mpg, on one trip to/from work (about 30 miles) I can eat up about a gallon of gas in 30 mins.

[jetmechmarty]

I doubt that it's the vent, otherwise the other side would show the same symptoms too.

Don't be so sure! What did you used for a filter in the cap when you replaced the old one?

[GLoweVA]

Don't be so sure! What did you used for a filter in the cap when you replaced the old one?

A little piece of scotch-bright pad.

If I had another key, I'd open it up next time it happens, but alas that is not the case. (maybe I could try one of my other bike keys.....)

[TopCatGr58]

Hey George,

The fuel lines running BELOW the carbs/intakes to the level of the starter motor and then back up isn't ideal! I have mine crossed so left petcock feeds right and vice versa, and have the hoses running across the top of the intake/pods, and only dip to the level of the bottom of the carbs at most.

Also, junk can build up in the "T" fitting between the carbs and restrict flow there so that the gas gets to the "T" but then can't get easily past it into the actual bowls! Good Luck.

T.C.

[ViperRon]

I routed my lines lower than bowl once and had the same issues you have developed, problem gets worse if tank gets below half full.

[MPittma100]

Fuel Delivery

The openings in the tank for the petcocks are supposed to be small enough to press on the filter stands (holding them in place) when you bolt the petcocks up to the tank.

I have seen one side on one tank where the opening was too big and allowed the filter stand to get loose and roll around in the tank. Foreign objects then partially blocked the petcock causing a similar problem. This is rare, but those filters need to be checked.

Mike

[CaptonZap]

[On the special tank (3.9 gal) and about 35mpg, on one trip to/from work (about 30 miles) I can eat up about a gallon of gas in 30 mins.

32 oz is a quart, in 7 1/2 min.
Thats 4.2 oz per minute
Let's call it a cup every two minutes.
Either side should flow that much.

CZ

[GLoweVA]

32 oz is a quart, in 7 1/2 min.
Thats 4.2 oz per minute
Let's call it a cup every two minutes.
Either side should flow that much.

CZ

Damn CZ, I'm an engineer and I hadn't even thought to reverse math my consumption to come up with a guideline to see how much flow I should be getting. THANKS.