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View Full Version : Carb/PCV/Intake help needed QUICK!!!


Matt L.
05-20-2011, 09:28 PM
Dropped on a new Edelbrock marine carb on this afternoon.

OOPS no PCV Vacuum port on it!!!

What to do, no port in the carb spacer either.

There is a blocked off port in one of the intake manifold runners I have placed a barbed fitting into it and looks like it will function as a temporary fix for the weekend. This is likely an unused power brake vacuum port for auto applications.

?????? Will this cause that cylinder to run too lean????

Any other suggestions. Wife is getting pissy and wants to leave for the lake!!!

Thanks,

Matt

airdrew99
05-20-2011, 09:38 PM
Got any pics? Plumbing into the intake should not cause it to lean too much. If you think about, when the vacuum port is in the spacer (between the carb and intake), it is no different than an intake vacuum because it is down stream of the air fuel mixture. Some edelbrocks have a vacuum port on the lower rear side, but that might be auto and not marine. I haven't messed with marine edelbrocks yet.

Drew

Matt L.
05-20-2011, 09:46 PM
Drew,

Thanks.

This port is about half way down a single runner. So I'm thinking that cylinder will be pulling extra air from the PCV rather than evenly distributing the PCV air to all cylinders.

I'm afraid it will cause that cylinder to run really lean and potentially damage the engine.

I just need to get through the weekend and I'll drill and tap the carb spacer next week.

Thanks,

Matt

airdrew99
05-20-2011, 09:49 PM
Sorry, I didn't read it close enough. If it is on a single runner (mid-way down runner or further), than this could possibly cause a lean condition in that one cylinder. Is there any other ports to use higher on the intake manifold?

Drew

j.mccreight@hotmail.com
05-20-2011, 09:55 PM
Why would it lean out a single cylinder because of a vacuum port? Take a look at gm trucks, fords they all used manifold vacuum from different places mostly for ease of accesibility it wont lean out a single cylinder so you'll be fine

airdrew99
05-20-2011, 10:00 PM
If it was a vacuum port going to something like a brake booster, then it wouldn't add more air to the engine. However, a pcv valve allows a steady flow of air to enter that particular intake runner causing a lean condition (because only air is entering, but no more fuel).

Drew

Matt L.
05-20-2011, 10:03 PM
If it was a vacuum port going to something like a brake booster, then it wouldn't add more air to the engine. However, a pcv valve allows a steady flow of air to enter that particular intake runner causing a lean condition (because only air is entering, but no more fuel).

Drew

Exactly what I was thinking. But is it enough to matter for 2 days of running around the lake. Probably won't even ski/board much. Just an easy weekend at the lake.

Don't want to fry a cylinder though.

Matt

j.mccreight@hotmail.com
05-20-2011, 10:17 PM
so your saying because of a vacuum port on one runner will lean out a cylinder, what about all the edelbrock, weiand, holley etc manifolds that only have one vacuum port what about the tbi fuel injected manifold or mpi injected engines?? one on left is the tbi injected engine the right is a carburated 350,

JimN
05-20-2011, 11:09 PM
Why would it lean out a single cylinder because of a vacuum port? Take a look at gm trucks, fords they all used manifold vacuum from different places mostly for ease of accesibility it wont lean out a single cylinder so you'll be fine

If you look at all of the early MC TBI motors, they had the PCV hose going to the #8 runner and they stopped because they had a big problem with that cylinder running lean, so....

That cylinder would automatically have less vacuum/more air going to it because the PCV valve would act like a slightly controlled vacuum leak and that makes it a problem. They learned from the mistake- these are run at higher average RPM than a car or truck during normal driving and that's why it didn't cause problems.

j.mccreight@hotmail.com
05-20-2011, 11:47 PM
fair enough ...

Matt L.
05-21-2011, 02:26 AM
If you look at all of the early MC TBI motors, they had the PCV hose going to the #8 runner and they stopped because they had a big problem with that cylinder running lean, so....

That cylinder would automatically have less vacuum/more air going to it because the PCV valve would act like a slightly controlled vacuum leak and that makes it a problem. They learned from the mistake- these are run at higher average RPM than a car or truck during normal driving and that's why it didn't cause problems.

As I suspected! However, it sounds like 1 light weekend of boating won't likely result in a wrecked engine.

agree or disagree???

Thanks,

Matt

PS Got the new carb on, fired right up and sounds great! We'll see how she runs in the AM.

Kyle
05-21-2011, 04:09 AM
A vacuum leak at idle will cause higher Rpm's.

Since we run such high rpm when running the engine creates less vacuum as Jim said. Have a fun weekend ski a set for me. You will be fine.

Let us know Monday if you have a hesitation or a fall on your face out of the hole problem. You should be fine though.

Matt L.
05-21-2011, 10:21 AM
Thanks to all for the quick reply and piece of mind that I'm not frying a cylinder.

Headed out, I'll let you know how it does.

Later,

Matt

JimN
05-21-2011, 10:55 AM
Thanks to all for the quick reply and piece of mind that I'm not frying a cylinder.

Headed out, I'll let you know how it does.

Later,

Matt

As long as you're not in a place that's extremely hot and dry, you should be fine.

Matt L.
05-23-2011, 02:35 AM
As long as you're not in a place that's extremely hot and dry, you should be fine.

Now you tell me!!!

Ran pretty well. I did have an occasional stumble out of the hole. We'll see how next weekend goes with a new carb spacer in.

Thanks for the help!

Matt

Kyle
05-23-2011, 03:10 AM
Are you sure that the air fuel mixture screws are set to your proper settings. If you buy a carb and it's tested in Florida and you live in Colorado yes the carb is still new or rebuilt but settings will change.

If you are using the same carb your intake swap will change the characteristics of air fuel mixture.

Bet a little of tweaking on that carb and the slight hesitation will go bye bye.

Matt L.
05-24-2011, 10:41 AM
Are you sure that the air fuel mixture screws are set to your proper settings. If you buy a carb and it's tested in Florida and you live in Colorado yes the carb is still new or rebuilt but settings will change.

If you are using the same carb your intake swap will change the characteristics of air fuel mixture.

Bet a little of tweaking on that carb and the slight hesitation will go bye bye.

I'm going to play around with it on Friday at the lake. The idle mix screws are out of the mix as soon as you come off idle so I'm not quite sure where to go from there. May call Edelbrock's 800 number ad see what they suggest.

I'm chasing a new carb spacer with a PCV vacuum connection in it today.

Thanks again!

Matt

thatsmrmastercraft
05-24-2011, 10:46 AM
Aside from a little tweaking of the mixture screws, you may be changing main jets and the accelerator pump stroke. Definitely call the Holley 800 number. They will be able to advise you on what high altitude adjustments you need to do to get you in the ballpark, and can walk you through the fine tuning.

CantRepeat
05-24-2011, 10:52 AM
I'm going to play around with it on Friday at the lake. The idle mix screws are out of the mix as soon as you come off idle so I'm not quite sure where to go from there. May call Edelbrock's 800 number ad see what they suggest.

I'm chasing a new carb spacer with a PCV vacuum connection in it today.

Thanks again!

Matt

How did you adjust the idle screws, with a vacuum gauge and your tach?