exhaust issues
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New User
Joined: Jun 2005
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From: florida
exhaust issues
I replaced my old 289 in my 68 bronco with a new ford 302 crate engine.
The only thing I didn't replace was the old headers...not sure what age they are...probably the 80's? I have a 6 year old Holley 4 barrel carb. and an old exhaust piping system.
I have good idling for periods after adjustment...but then it seems to slip back in a low idle mode. I also have a strong gas smell and large amounts of black smoke mostly when I start it from cold. Then light amounts of black smoke as I am cruising around town.
What do you think the issue is? Not the proper flow through? too rich in the air fuel mix?
I just want to make sure I am fixing the right thing.
thanks
The only thing I didn't replace was the old headers...not sure what age they are...probably the 80's? I have a 6 year old Holley 4 barrel carb. and an old exhaust piping system.
I have good idling for periods after adjustment...but then it seems to slip back in a low idle mode. I also have a strong gas smell and large amounts of black smoke mostly when I start it from cold. Then light amounts of black smoke as I am cruising around town.
What do you think the issue is? Not the proper flow through? too rich in the air fuel mix?
I just want to make sure I am fixing the right thing.
thanks
Elder User
Joined: Sep 2007
Posts: 521
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From: new mexico
that is first place to look...choke
power valve maybe next,
is the float sticking ??
did you let the carb sit for a long time before you used it again.
did you rebuild it...
i love holley carbs but really only use them on really big performance engines.
my 289 68 Bronc. un-rebuilt had a a/market holley 2bbl.
put a auto/2100 about 2 yrs ago and it is more in tune with the engine.
holley really did make it smoke more but never tried to re-jet it.
i am at 4000+ ft though and needs to be jetted for the altitude...
any help?
power valve maybe next,
is the float sticking ??
did you let the carb sit for a long time before you used it again.
did you rebuild it...
i love holley carbs but really only use them on really big performance engines.
my 289 68 Bronc. un-rebuilt had a a/market holley 2bbl.
put a auto/2100 about 2 yrs ago and it is more in tune with the engine.
holley really did make it smoke more but never tried to re-jet it.
i am at 4000+ ft though and needs to be jetted for the altitude...
any help?
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Joined: Jun 2005
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From: florida
Thanks for the help friends...I will inspect the choke and see how that works. I have assumed that the air mix screws when tightened would lessen the air mix and make it run richer, but by screwing them in a touch I did cut out the black smoke. I will see if that lasts...I think the shake of the engine makes them loosen over a short period? Any suggestions with keeping the tuning in place?
I did think about putting a more moderate carb. on there to maybe even help reduce gas consumption and see if that helps.
Do you recommend going to the 2bl. carb...any other suggestions?
I did think about putting a more moderate carb. on there to maybe even help reduce gas consumption and see if that helps.
Do you recommend going to the 2bl. carb...any other suggestions?
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From: Southern Oregon USA
A properly tuned 4 bbl will offer better economy over a 2 bbl. In most cases, the primaries on a 4 bbl are smaller so they will be more efficient. That's if you can resist the urge to stay out of the secondaries.
Jason
Jason
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Joined: Oct 2005
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Try a new power valve before you do a complete rebuild. They can go bad... for no reason.
I had one fail on me for absolutely no reason. I used my Bronco for some errands, then parked it for an hour and a half at the house and then when I turned it over to hit the road again..... totally blown power valve. Always keep two or three on hand.
Try this.... turn the truck over and then turn the two idle mixture screws in until the seat, or will not turn in anymore. Count the turns as you do this. Do this gently! If your truck keeps running with both seated your power valve is blown.
Keep track of the turns. How many?
If it has a blown power valve then next thing you really want to check is the oil. Pull the dipstick out and smell that oil. If it smells like gas you want to change it ASAP. You don't want to run the gas impregnated oil too long because you run the possibility of taking out a bearing in your engine. If you have a non-roller cam in that engine you need a special break in lube from Comp or Crane for cams with todays oils and look at maybe Shell Rotella oil too.
I had one fail on me for absolutely no reason. I used my Bronco for some errands, then parked it for an hour and a half at the house and then when I turned it over to hit the road again..... totally blown power valve. Always keep two or three on hand.
Try this.... turn the truck over and then turn the two idle mixture screws in until the seat, or will not turn in anymore. Count the turns as you do this. Do this gently! If your truck keeps running with both seated your power valve is blown.
Keep track of the turns. How many?
If it has a blown power valve then next thing you really want to check is the oil. Pull the dipstick out and smell that oil. If it smells like gas you want to change it ASAP. You don't want to run the gas impregnated oil too long because you run the possibility of taking out a bearing in your engine. If you have a non-roller cam in that engine you need a special break in lube from Comp or Crane for cams with todays oils and look at maybe Shell Rotella oil too.
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New User
Joined: Jun 2005
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From: florida
All great comments...thanks...I will stay with the 4brl then if it will get me better economy, especially with gas prices right now.
On the other hand...when I screw the idle mixture screws in the engine does stall...so does that mean the power valve is cool? I did almost completely reduce the black smoke out of the exhaust when I adjusted the screws both to one full rotation out of full seat. I had to adjust the idle throddle to keep it from stalling...but it seems to be better...but the engine runs a bit longer after I turn off the ignition?
I will check the oil for smell...I probably will just change it anyway.
I am still not sure if what the problem is...I dont seem to have the top end when I floor it at 30mph? I do have performance roller rockers.
On the other hand...when I screw the idle mixture screws in the engine does stall...so does that mean the power valve is cool? I did almost completely reduce the black smoke out of the exhaust when I adjusted the screws both to one full rotation out of full seat. I had to adjust the idle throddle to keep it from stalling...but it seems to be better...but the engine runs a bit longer after I turn off the ignition?
I will check the oil for smell...I probably will just change it anyway.
I am still not sure if what the problem is...I dont seem to have the top end when I floor it at 30mph? I do have performance roller rockers.