77 Bus - 36 IDF Carbs Are Flooding! FIXED!

[Sluggo]

Same carbs, engine, pump & everything from my '72 (except the tranny). When they were in the '72 I got 20-23 MPG highway and 17 city. Now I get about 17.5 Highway & 12 city. All carb gaskets have been replaced except the carb top gaskets. Noticed a small leak (gas residue) all around the carb top gasket on both carbs. All the other gaskets are nice & thick but the top gaskets are very thin paper. All the replacements I see are also thin paper.

1. Could this cause my mpg issue?
2. Are there thicker gaskets or a way to make sure the carb top seals to the body? Can I cut my own thicker gasket?

[RSorak 71Westy]

Do any of the brakes on the new drag? Is the final drive ratio different from a 72 to 77? Did you change tire sizes? Is a 77 bus much heavier than a 72?

[Sluggo]

Do any of the brakes on the new drag? Is the final drive ratio different from a 72 to 77? Did you change tire sizes? Is a 77 bus much heavier than a 72?

I do feel occasional drag on the new but not that much and it's only after lot's of brake use (mountains & stuff) which is rare. I believe the ratio is different. "Freeway Flyer" tranny. I don't know if a stock '77 is heavier but I added lots of e-dead. Maybe 150lb added weight. But then leave out all the tools & crap I used to carry and it probably evens out.

[Amskeptic]

Do any of the brakes on the new drag? Is the final drive ratio different from a 72 to 77? Did you change tire sizes? Is a 77 bus much heavier than a 72?

I do feel occasional drag on the new but not that much and it's only after lot's of brake use (mountains & stuff) which is rare. I believe the ratio is different. "Freeway Flyer" tranny. I don't know if a stock '77 is heavier but I added lots of e-dead. Maybe 150lb added weight. But then leave out all the tools & crap I used to carry and it probably evens out.

You have different gear ratios now. The thin paper gasket is supposed to be a thin paper gasket. Install thee a new-to-you fuel injection set-up. Expect the factory fuel mileage. 16-20 mpg. The better power comes at a price.
Colin

[Sluggo]

You have different gear ratios now. The thin paper gasket is supposed to be a thin paper gasket. Install thee a new-to-you fuel injection set-up. Expect the factory fuel mileage. 16-20 mpg. The better power comes at a price.
Colin

I'll order the thin paper gasket from Aircooled.net I guess. All the other sites I see just sell the whole rebuild kit.

FI is what we will be doing on your next visit. If I can afford it I'll get a second day to do the front torsion arms.

[Sluggo]

Got my carb top gaskets from Aircooled.net. Have to say they are the best I have seen. Nice & thick. 2-3 times thicker than all the others I've seen. We'll see how well it works.

I'll get a chance to use my new digital caliper to check my float levels too!

[Sluggo]

Finally got a chance to install the new carb top gaskets & reset my floats. The floats were at 9.5mm & 28mm. Reset them to 11mm & 20mm. Cleaned up the tops & internal filter while they were off. Had to cut holes in the gaskets for the idle jet holders but other than that they are a great fit and very well made. Better than the ones that come in the rebuild kits!

Started her up and she ran like crap. Wouldn't hold idle at all. Had to rev and run to the back several times before I made it in time to hit the the throttle and keep it from stalling. Then I noticed the black exhaust. Couldn't believe it was that rich but tried closing the mixture screws a 1/4 turn (they were at 2 - 2 1/2 turns out). barely better but still won't idle. Go in another 1/2 turn, better but still won't stay running. Kept going until they were almost closed. barely 1/8 of a turn out. Running great! No popping or hesitation. Idle is a little low but I can fix that. Ran even better with the mixture screws only a hair open! I put them out to 1/4 turn just because a hair doesn't seem right. At 1/4 turn out if I do the brake pedal test my RPMs go up about 150.

Holy $h!t! Could carb top gaskets cause that extreme of a leak. They are about 3 years old and have been removed 5 or 6 times but I didn't think they could leak that much. Can't wait to see what my mileage is!

[Amskeptic]

The floats were at 9.5mm & 28mm. Reset them to 11mm & 20mm.
Kept going until they were almost closed. barely 1/8 of a turn out.
Could carb top gaskets cause that extreme of a leak.

Why do you have two readings for float levels? I am suspecting that the thicker gaskets have raised your float levels an unhealthy amount and gas is pouring into the emulsion tube and outlet orifices with very little air flow. Remember, these floats are like a toilet tank where the tank cover holds the shut-off valve. If the cover is now sitting on a thick gasket, the shut-off valves are that much higher too.
Colin

[Sluggo]

The floats were at 9.5mm & 28mm. Reset them to 11mm & 20mm.
Kept going until they were almost closed. barely 1/8 of a turn out.
Could carb top gaskets cause that extreme of a leak.

Why do you have two readings for float levels?

The high level & low level.

I am suspecting that the thicker gaskets have raised your float levels an unhealthy amount and gas is pouring into the emulsion tube and outlet orifices with very little air flow. Remember, these floats are like a toilet tank where the tank cover holds the shut-off valve. If the cover is now sitting on a thick gasket, the shut-off valves are that much higher too.
Colin

Float levels were set with the gasket on so the levels should be the same. A few years ago I was working with some of the performance carb Gurus at ShopTalk Forums and was told that (with Weber IDFs) if you only have to barely crack the mixture screws and get great performance/mileage you are good to go. I had forgotten this bit of advice until I reread it this morning. I'll turn them back in, do brake pedal test, watch the temps/mileage and see how it goes.

[Sluggo]

With the mixture screws out about 1/8 turn each I seem to be best. Performance is amazing! Throttle response is immediate & powerful! Truly the best the engine has ever performed. It was really good before but now it's phenomenal. No popping on deceleration like it used to. It used to diesel (run on) so I had to shut it down like a diesel engine. Haven't had to do that since. The exhaust even smells better.

I can't judge the mileage yet because, sadly, I haven't had enough $ to fill the tank until today. I'll post the results after a few days.

I'll be changing out the idle jets from 55 to 50 & the mains from 135 to 130 just as an experiment. I already have a bunch of different jets so might as well.

Hope my mileage improves as much as everything else!

Colin,

The gasket wasn't as thick a say the base or manifold gaskets. Just thicker than the ones that come in the kits. The old ones were like a sheet of construction paper thick and the new ones are like 2 1/2 sheets thick. Since I set the floats with the gaskets in place I think the level should be the same either way.

[Sluggo]

So the engine is still running beautifully but I'm still getting crap for mileage. The truly odd thing is that the mileage is fluctuating between 8.5MPG & 13MPG. This is with no changes being made in the last week & a half.

Before this I had replaced a bad float & fixed a vacuum leak. Better performance but mileage still sucks. I also played with the jets. Mileage stayed the same but performance suffered. Brought it back to good performance but still horrible mileage. Head & Oil temps are perfect.

[Amskeptic]

So the engine is still running beautifully but I'm still getting crap for mileage. The truly odd thing is that the mileage is fluctuating between 8.5MPG & 13MPG. This is with no changes being made in the last week & a half.

Before this I had replaced a bad float & fixed a vacuum leak. Better performance but mileage still sucks. I also played with the jets. Mileage stayed the same but performance suffered. Brought it back to good performance but still horrible mileage. Head & Oil temps are perfect.

You are dealing with obvious mis-matched engineering. You need to dump all that gasoline in to get any work done. Something is relatively horribly awry. Like urban traffic.
Colin

[Sluggo]

You are dealing with obvious mis-matched engineering. You need to dump all that gasoline in to get any work done. Something is relatively horribly awry. Like urban traffic.
Colin

The same equipment (carbs, engine, pump, filter I've been using for 4 years now. Never ate gas like this before. It doesn't need all that gas (it didn't before). It's just getting it and I can't figure out why. What are the signs of a bad needle & seat?

[Ryno]

What are the signs of a bad needle & seat?

One surefire sign is an over-filled crankcase with oil that is thinned out and fuel smelling.

[Sluggo]

What are the signs of a bad needle & seat?

One surefire sign is an over-filled crankcase with oil that is thinned out and fuel smelling.

Been checking at least every other day. Not happening. Today I checked for leaking fuel fill hose & cap and they are dry too. My pump has an anti-siphon so it wouldn't keep flowing anyway.