Rochester 4jet
 

Installed Rochester 4jet 53 olds on a 51 merc stock flathead. Runs fine for about 30 seconds then starts to die pump throttle to keep it running then rough running and popping thru exhaust. Motor 12v with MSD dist. Thanks to anyone that can help.

Re: Rochester 4jet
 

Bill,
Did you get the email I sent you with jet sizes and float settings ?
How did it run prior to the carb change ?
There are a couple dinky filter screens in the carb...one in the fuel inlet
and one in the bottom of the bowl near the accelerator pump. Obviously if these
are partially plugged that will give the results you are experiencing. Get rid of these
and try it ( use an inline filter in their place ).
Somewhere in the back of my mind I'm wishing to tell you to reinstall
your points dist with the proper coil if things seem ok with the carb. Cheap 12v coil
Carquest 26231 w/ int resistor will get back to basics. Don't forget if you are running
pos ground the pos side of the coil is attached to the dist...you guessed it neg grd
neg side of coil to dist.
I'm quite fond of these vintage Rochesters and look forward to following
your progress. Guys lots better than me are here to help git 'er done.
Charlie ny

Re: Rochester 4jet
 

Charlie Thanks for providing the th infor on the screens. Will remove them this weekend. Hope that is the problem. I love the look of the carb but close to giving up as I have spent close to a month trying to get it to run. I did not rec eive your infor thru gmail. It was running fine before carb swap so aim a little puzzled about replacing the MSD back to org dizzy. Thank you very much for your expertise.

Re: Rochester 4jet
 

Charlie once posted a 'sort-of' tutorial on these carbs, or, at least it was some of his experience with them. Wish I could find it now. In-any-event, I'm also using one, and offer the comment that when running right, it's one of the smoothest carbs I've experienced. (For comparison, I also have one car with a Carter WCFB, and it has never run right from the day it was new. I need a 'Charlie' for the WCFB.)

Re: Rochester 4jet
 

Bill,
My suggestion about the dist was IF after wringing out the carb you might
go back to points just to eliminate ignition.
Here's the specs I sent about my setup:
Primary jets 51's
Secondary jets 56's
Front and rear float setting 1.687
Plug the power valve and the vac circuit that actuates
the PV plunger
The above was developed with the aide of a broad band A/F meter, not the
seat of my pants. It's been 3 years give or take a bit and all I've done is wipe the
grime of the carb occasionally.
Don't give up on this Rochester...feel free to call me after 7 pm est anytime,
716 662 9159.
Charlie ny

Re: Rochester 4jet
 

I can 'plug the vac circuit that actuates the PV plunger', but I am not clear on how to 'plug the PV'. Suggestions?? Do you mean to drive something into the PV to plug the 'orifice'? Or?

Re: Rochester 4jet
 

Do not drive anything into anything. I soldered the PV closed and reinstalled it
The A/F meter was telling me I was way too rich at top end and this was a sort of big step to determine in what direction to proceed.
Charlie ny

Re: Rochester 4jet
 

Also, if you drive small lead shots into the side holes of the power valve, they can be removed later if you decide you need the power system on you're engine. If you solder it shut, the heat will destroy the small spring in the power valve, and render it strictly a plug.


Charley ny, the engine you're 4GC originally came off of probably needed a steeper tilt to the WOT air/fuel curve, and would be my guess why when on you're engine it was too rich at the top end. If you verified you're calibration with an air/fuel meter then it obviously works on you're engine without a power system. Good job.

Sal

Re: Rochester 4jet
 

Sal,
Yep it goes like stink !!
I have collected a box of these Rochester PV's ,various #'s, if in need give me
a hoot.

Charlie ny

Re: Rochester 4jet
 

Charlie,

The Rochester 4gc that I have at home ('65 Olds) has a power valve with 4 large side holes (look to be around .090" each), so I'm assuming the power jet restriction is in the bowl somewhere after the power valve. I didn't realize they had numbered valves too.
Maybe earlier in the 50's ? Can you clear me up on this ? Always want to learn.

Sal