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Old 07-10-2006, 08:27 PM   #1
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Default engine air leak??

my engine is behaving eratically, after full throtle the rpms stays high for a couple of seconds and then goes back to idle, been playing with the needles for a while and nothing, some body told that i may have an air leak, what would be the best way to find out if my engine has an air leak? what could be causing this problem?
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Old 07-10-2006, 08:41 PM   #2
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Could be many things. Airleak is a good possibility. Or could be to high idle and to rich of low speed setting. Best place to start is reset the idle with filter off, then set the needles to stock settings and retune from there. If it still doesn't tune right it's time to check the fuel tank, lines, and reseal the engine. Going back to stock needle settings and retuning is much easier/faster/productive than chasing a tune after the needles have been played with multiple times.

As for checking for air leaks, well if it doesn't tune and the engine isn't worn out it's best just to replace the fuel lines, take the engine apart/clean it and seal it up with some sensorsafe orange rtv from the auto store. Seal the backplate, under the carb, around the banjo fitting where your fuel line connects to. After doing that it should be fine. Also check the manifold gasket to make sure it's in good condition as well as the oring on the fuel tank.
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Old 07-10-2006, 10:01 PM   #3
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Default Bubbles

Paint the outside of the engine with dish soap, connect a fuel line to the carb, plug the carb air intake and exhust port with finger and blow through the hose.

Jim
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Old 07-10-2006, 11:35 PM   #4
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thanks
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Old 07-12-2006, 02:45 AM   #5
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Quote:
Originally Posted by jbrow1
Could be many things. Airleak is a good possibility. Or could be to high idle and to rich of low speed setting. Best place to start is reset the idle with filter off, then set the needles to stock settings and retune from there. If it still doesn't tune right it's time to check the fuel tank, lines, and reseal the engine. Going back to stock needle settings and retuning is much easier/faster/productive than chasing a tune after the needles have been played with multiple times.

As for checking for air leaks, well if it doesn't tune and the engine isn't worn out it's best just to replace the fuel lines, take the engine apart/clean it and seal it up with some sensorsafe orange rtv from the auto store. Seal the backplate, under the carb, around the banjo fitting where your fuel line connects to. After doing that it should be fine. Also check the manifold gasket to make sure it's in good condition as well as the oring on the fuel tank.
Orange rtv silicone is for backyard auto mechanics! If you have to use it, make sure to use it sparingly as too much can lead to blockages internally inside the engine, and this is not good (especially in the carb intake area). And using it near the fuel fitting is definitly not a good idea.

It is a better idea generally to replace the orings and gaskets in question with new ones to achieve an airtight engine. Leave the RTV for the beat up '71 pinto broke down in the backyard!

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Old 07-12-2006, 03:45 AM   #6
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Default Air leak

The last time i had this happen it was the o ring on the fuel tank. I could hear mine leaking when i blocked the fuel line and blew in the the other line.
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Old 07-12-2006, 07:07 AM   #7
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Quote:
Originally Posted by mxwrench
Orange rtv silicone is for backyard auto mechanics! If you have to use it, make sure to use it sparingly as too much can lead to blockages internally inside the engine, and this is not good (especially in the carb intake area). And using it near the fuel fitting is definitly not a good idea.

It is a better idea generally to replace the orings and gaskets in question with new ones to achieve an airtight engine. Leave the RTV for the beat up '71 pinto broke down in the backyard!

BK
Each there own... You're the first I've ever had disagree with me on that.
Use a toothpick to put it on and there's no problems.
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Old 07-12-2006, 07:39 AM   #8
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Can someone help me with this? my car will run great in the race heats but when it comes to the 10min. main and i go to pit it will stall.this drops me out of 1st. place every time this is killing me! (am i to lean on the low to rich on the high?) i'm lost, help.
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Old 07-12-2006, 09:00 AM   #9
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Quote:
Originally Posted by jbrow1
Each there own... You're the first I've ever had disagree with me on that.
Use a toothpick to put it on and there's no problems.
I have found many engines that have been 'sealed' this way with alot of globbed up rtv inside, some so bad that the intake is partialy blocked. Also putting rtv on the fuel fitting is definitely asking for trouble in the carb, if this gets inside it will be very hard to correct.

I have alot of experience working on full scale racing motorcycle engines at the factory racing level, and I think if you ask any Race engine mechanic about using RTV they will tell you the same thing. Engines are designed to be leak free without the use of sealant (except for a few exceptions, such as crankcase halves which need sealant because the crankcase is designed to have no gasket between the two pieces. The crankcase splits the main bearing journals and having a gasket between them would cause poor main bearing fitment, as the gaskets usually have poor control of squish, causing the bearing clearance to be unstable.)

Oh and V8 car engines intake manifold, where the manifold meets the heads!

I guess my message is, engines are designed to use gaskets not sealant (for the most part) but if rtv is necesary, use it VERY sparingly, as a little goes a long way to seal.

Also use good judgement when you apply it, do so, so that no excess can work it's way inside the engine. And then by all means wait for the selant to cure completely before running the engine, as the engine can suck this goop inward to the crankcase if the engine is started before the selant is dry. This is a bad thing!!

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Old 07-12-2006, 09:05 AM   #10
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Quote:
Originally Posted by RANDY SMOOTH
Can someone help me with this? my car will run great in the race heats but when it comes to the 10min. main and i go to pit it will stall.this drops me out of 1st. place every time this is killing me! (am i to lean on the low to rich on the high?) i'm lost, help.
I would guess too rich on the LSN. When the engine is hot, the mixture requires less fuel for the same ratio.

Just be sure that the engine is at FULL operating temp when you set up the LSN and you should be good. Once the engine is run for 4 min, at speed, pull the car off the track and then set the LSN using the pinch test, this should get you an engine that will purr like a kitten when you come in for a pit, unless the HSN is too lean, then it will hold high idle, similar to an air leak.

Alot of guys will run too rich LSN because the engine was adjusted when it was cold, or they are masking an air leak (unknowingly)

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Old 07-12-2006, 09:08 AM   #11
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Thanks man i'll give that a shot.
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Old 07-12-2006, 12:56 PM   #12
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Default Flame out after refueling

Another problem you may consider is that after refueling the car Fuel can get in the pressure line and it will starve the engine. If you install a pressure chamber between the pipe and the tank it may cure your problem.I have had this happen to me just last week. It can also be very hard to restart after it flames out because the heat from the hot engine transferrs to the carb and causes vapor lock. Hope this helps.
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Old 07-12-2006, 02:04 PM   #13
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Quote:
Originally Posted by RANDY SMOOTH
Can someone help me with this? my car will run great in the race heats but when it comes to the 10min. main and i go to pit it will stall.this drops me out of 1st. place every time this is killing me! (am i to lean on the low to rich on the high?) i'm lost, help.
Sounds like your carb is getting too hot causing the fuel to boil out which makes the engine flame out.
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Old 07-12-2006, 02:55 PM   #14
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Thanks you guys. My v-one rrr will stay on top this weekend.
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