Rods 'n' Sods - UK Hot Rod & Street Rod Forums banner

1 - 7 of 7 Posts

·
Registered
Joined
·
275 Posts
Discussion Starter #1
Since I fitted the new q-jet carb to the 350, its been running rich, tired everything I can untill today when I fitted some smaller jets. I thought I had transfared everything from the old carb but Im not sure if I mixed the jets up.

So it had 77 jets in, tonight I fitted 55 jets,but I still had to wind the mixture screws all the way in according to my friends old CO meter to get it to 2%

Here is the plug after 10 miles motorway then 5 miles on B roads, my old man always said the plug will tell you if its running right.

 

·
Registered
Joined
·
12,494 Posts
Try running at constant 50 mph for say 5 minutes - knock in to neutral - cut engine and coast to a stop - pop plugs out and the compare.
 

·
Turbo 4 pot freak
Joined
·
1,891 Posts
To be honest trying to screw these old style engines down to 2% co may be not the best setting for your engine see what is happening to the H/C's, you need to tune it for smoothness and keep a careful eye on the H/C reading getting them nice and low. Sometimes I have found running the H/C's as low as they will go with the engine running the smoothest if you can get the H/C's down in the 100ppm to 200ppm range the Co may settle nicely with a good smooth idle, then see what the co is reading and you may be pleasantly surprised and find it is nice at 4%, if you have a lowish compression engine the readings will probably pan out higher to get it running nice.

John
 

·
Exceeded sell by date
Joined
·
7,739 Posts
I'm very much with John here. We used to set up mechanical injection V8's on the dyno at work. Some of those engines were running their best at an idle of 6% co. and that was the factory setting. Carbed Chevy engines generally sat at a best of 3.5 - 4% depending upon spec, with some only occasionally going lower.
 

·
Registered
Joined
·
727 Posts
Is it a new Qjet? If not it may have the very common leaky fuel wells on the bottom of the carb, Dont like saying this but, google the Qjet fuel leak or well leak or some such, you'll find the answer lots quicker than me talking you through it. 77's to 55's is a big jump, hence me thinking its getting petrol from somewhere it shouldn't.
Worth a look,
Martin.
 

·
Registered
Joined
·
275 Posts
Discussion Starter #6
Is it a new Qjet? If not it may have the very common leaky fuel wells on the bottom of the carb, Dont like saying this but, google the Qjet fuel leak or well leak or some such, you'll find the answer lots quicker than me talking you through it. 77's to 55's is a big jump, hence me thinking its getting petrol from somewhere it shouldn't.
Worth a look,
Martin.
The carb was a recon unit of ebay, all the wells on the carb have been epoxied.
 

·
Registered
Joined
·
275 Posts
Discussion Starter #7
Well I decided to take things back to the basic's, which is what I should of done in the first place, my static timing was at 25 deg btdc, I also think there is wear on the mechanical advance. The mechanical advance that is still on stock springs and doesnt get to full advance before red line anyway.

Ive got a good video on my build thread tho of how its running now :crazy:
 
1 - 7 of 7 Posts
Top