The Jensen Owners' Club A technical and discussion forum for all Jensen enthusiasts It is currently Mon Dec 09, 2019 9:54 am

V-8 Engine Tech

ThermoQuad accelerator pump problems

Mopar Big Block Talk

by RayR » Thu Jan 10, 2019 2:38 am

Hi, looking for some advice on the Thermoquad carb accelerator pump. I have a Summit rebuilt TQ on my Mk III interceptor (Replaced a Carter AVS which replaced the original TQ) and have just had my second accelerator pump failure - pump operates and nothing out of the nozzle cluster. The first time I tracked it to the 'rubber' pump cup which had partially disengaged from the plastic 4-pronged holder and was 'flapping' during the pump stroke. I happened to have a spare for my original TQ and fitted that which seemed to be tighter on the holder and all good. Now it has failed again and this time I have traced it to a 'leak' past the one way valve housing at the bottom of the pump - I operate the pump manually in a bowl of petrol.
When I removed the pump assembly the one way valve (brass in the Summit carb) was not very tight so I thought i would replace it with the one from the original carb - however that just slipped in with no interference!!!
So, has anyone any experience with these accelerator pumps? could the rebuilt carb have had the pump bore enlarged? if so any clues as to where to get an oversize one way valve? or any other ideas? I guess the last option would be getting a different carb top casting?

Ray
MkIII Interceptor (140 8488)
User avatar
RayR
 
Posts: 190
Joined: Mon Mar 05, 2018 4:43 am
Location: New Zealand

by Hangtowner » Sun Mar 03, 2019 10:07 pm

Ray,
I have put kits into my TQ's many times and not had a problem. I have spare TQ's also. I can measure something if you want.
Hangtowner
 
Posts: 256
Joined: Wed Jun 07, 2006 12:38 am
Location: Hangtown, California

by RayR » Sun Mar 03, 2019 10:40 pm

Hi Hangtowner,

Thanks for the reply.

I have solved the fault, after the last episode when I took the carb top off and looked in the accel well the 'plastic' pump rubber had partially come off the 4 pronged support allowing fuel past when pumped, I took it out and it stayed in that position - see attached. At the same time I had ordered spares from mike's carbs, both leather and plastic. The new plastic ones were still 'loose' on the support so I put the leather one in - perfect. The old ones always had a slight hesitation on the pump now none at all with the leather version. The bore for the one-way valve is still a minor issue, I bought 2 spares at the same time - 1 basically fell in the hole and the other was a press fit!!! think they need to work on tolerances a bit!

Hopefully I am set for a few more years now!

Ray
Attachments
IMG_20190221_112652.jpg
IMG_20190221_112652.jpg (53.02 KiB) Viewed 339 times
MkIII Interceptor (140 8488)
User avatar
RayR
 
Posts: 190
Joined: Mon Mar 05, 2018 4:43 am
Location: New Zealand

by Moparguy » Tue Mar 19, 2019 12:48 pm

Daytona Carb .....Daytona FL USA has multi fuel compatible cups . Make sure you have a brass checkvalve as well . The original leather cups were best of course if there is a source for these .....In the USofA , it is common to have to "fix" "remanufactured" carbs of all types . Even with a high end $$$ supplier....
Moparguy
 
Posts: 18
Joined: Wed Jan 16, 2019 3:06 pm
Location: USA


Return to V-8 Engine Tech