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Quadrajet Base Gaskets

Scotcraft29

New member
Hi all - I'm new to this forum - hope I can some help..

I have a 29 Ft ScotCraft boat - with twin Crusader 270 engines. They have ReMfg Rochester Quadrajet Carbs ( 17010213 ) - The Intake Manifold is Spread Bore Plenum - 2 primary and 2 Secondary opening - the secondary bores are connected with a trough between them. They seem to run fine but on the rich side. I have had them tuned to specs but my issue is the Idle Adjusters seem to have no affect on the engine's idle and I get a noticeable gas smell from the exhausts.

The boat is winterized at this time and I pulled the carbs to rebuild on the bench. The kits come with Base Gaskets that are fully open. I am trying to eliminate as many issues as possible so my question is - should I be using a standard spreadbore gasket with 2 Primary and 2 Secondary holes instead of one large opening? I also see base gaskets that are almost 1/4 inch thick to handle heat - are these better than the regular cork type thin gaskets ?

I didn't detect any vacuum leaks on the intakes and I will check the fit on the carbs sections when I rebuild them.

I hope I've given all the info needed.

I value any suggestion here.

Thank you.
 
Welcome to ME.com!

You should be ok with either the 4-hole or the open gaskets...the thicker ones have more 'give' and are ideal for carbs that have a slight warp in their throttle plates. They can be used with true throttle plates as well...

When you say the 'idle adjusters seem to have no affect', are you referring to the idle mixtures screws? if so, at what RPM are you trying the adjustments?
 
Welcome to ME.com!

You should be ok with either the 4-hole or the open gaskets...the thicker ones have more 'give' and are ideal for carbs that have a slight warp in their throttle plates. They can be used with true throttle plates as well...

When you say the 'idle adjusters seem to have no affect', are you referring to the idle mixtures screws? if so, at what RPM are you trying the adjustments?

Hi Makomark and thank you for your response. I was leaning toward the 4 hole heavier gaskets since they cover more matting surface I just needed some positive feedback which you have given.

Yes, it's the Idle Mixture screws that I am trying to adjust. They sit well recessed in the base of the carbs ( I have the tool for them ) but no matter how many turns in or out - the engines don't respond. I am trying to get somewhere between 650 and 750 RPM in gear at warm idle. I have timing at 26 degrees BTDC at 3800 RPM. Odd thing about this is that if turn the Idle screws all the way in - the engines smooths out just a bit. To me - that says vacuum leak. This is why I asked the question about the heavier 4 hole gasket.
 
that suggests the throttle plates are opened such that the fuel is starting to flow from the transfer ports and you won't get any response from the idle mixture screws...I'd suggest, in the springtime, to try making the mixture adjustments at a lower idle speed.

you can also look for 'nozzle drip' in the primaries...you will see the fuel from the main nozzles puddling up on the top of the throttle plates...
 
Cliff Ruggles is the Rochester guru! May want to pick up his book and some rebuild kits directly from him. He has a forum as well with a great deal of helpful info. I rebuilt my Quads last year with his rebuild kits - they were spot on!
 
I would also suggest the 4 hole gasket.

Yes, it's the Idle Mixture screws that I am trying to adjust. They sit well recessed in the base of the carbs ( I have the tool for them ) but no matter how many turns in or out - the engines don't respond. I am trying to get somewhere between 650 and 750 RPM in gear at warm idle. I have timing at 26 degrees BTDC at 3800 RPM.
Your advance should be offering 26* much earlier than 3,800 RPM. In other words, if it requires 3,800 RPM to produce 26*, the BASE advance may be too low at idle speed.
Look to see what it's doing @ idle speed.

that suggests the throttle plates are opened such that the fuel is starting to flow from the transfer ports and you won't get any response from the idle mixture screws...I'd suggest, in the springtime, to try making the mixture adjustments at a lower idle speed.

you can also look for 'nozzle drip' in the primaries...you will see the fuel from the main nozzles puddling up on the top of the throttle plates...

Take heed to what Mark is suggesting.

Once the throttle plates open enough for the air horns to begin delivering fuel, the low speed fuel metering circuits have begun to drop out.
In the reverse of this......
the low speed fuel metering circuits to come into play only while the primary throttle plates are near idle position.
At this point, the air horns should not delivering fuel.
However, look for the "nozzle drip" that Mark mentioned.

Also, several of the Q-jet factory machining ports will be closed off with tiny welch plugs and epoxy sealant.
Look to see if the epoxy is failing.
When/if it fails, fuel may drip into the intake manifold plenum causing a rich mixture.
This may be why it is running rich, and why your low speed adjustment is not making any difference.
 
the jet well boring holes thru the base of the 170 series float bowls are sealed mechanically...I have yet to see one leak ....the 'old' 7x original castings used simple brass cup plugs and they were the source of this 'issue' even though the original solution was provided 50+ years ago...
 
the jet well boring holes thru the base of the 170 series float bowls are sealed mechanically...I have yet to see one leak ....the 'old' 7x original castings used simple brass cup plugs and they were the source of this 'issue' even though the original solution was provided 50+ years ago...

Ok - Thank you all - I will make copy of your replies and suggestions for early spring !

Thank you again !
 
One more thought, the throttle linkage can be a vacuum leak source. Cliff sells a bushing kit which solves this issue, I would recommend that if you want to go all in on this rebuild.
 
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