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Ongoing Problem: Engine Stalls When Put in Gear

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WhatISit View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WhatISit Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2018 at 12:52am


That’s the cam specs
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2018 at 8:36am
1978+ model 904s and 998s could be had with lock-up. Most were lockup from 78 on, but not all. AMC may not have got lock-ups until 79 or 80. Even then, CA six cylinder cars (at least for 78) didn't get lock-up converters nor did high altitude and HD models (from Allpar site, specifically referring to Chrysler products, but AMC would have been similar).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx2bfast Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2018 at 11:33am
The thumper cam is meant to sound like a race cam but has very little low end power. Generally will not create enough vacuum for power brakes. What stall converter are you running? You may need to get a higher stall so it can idle without a load. Probably need something in the 2800 - 3000 stall range to make it work. 
1975 gremlin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote auag85201 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2018 at 11:42am
with that cam and an automatic trans you will have a hard time getting it to idle in gear
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WhatISit Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2018 at 3:32pm
Yeah, I’m pretty much accepting at this point that the cam’s too much for my setup. I can make it work, but it’s still not going to be perfect, and it’s probably not going to have very good street manners.

According to the cam specs and the rest of my setup, Hughes gave me a 2500 RPM stall converter. I don’t know the details exactly, but I’m pretty sure the engine has 9:1 compression. I think comp cams could stand to update their information a little bit on the Thumpr. I’ve been reading everywhere that this cam is more aggressive than advertised. I could stand to have a 2800-3000 rpm converter and 10:1 CR.

We spent about two more hours today tuning the carb and setting the timing. Best we can manage is about 1100-1200 RPM in park, and 750-800 in gear.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2018 at 5:04pm
Nice mid range cam.
IMO to late on the intake closing timing for a 9:1 motor hooked to an automatic.
IMO (again) you would need a very loose converter for that to work.

There are few bandaids that can make it more drivable.

I would use a racing type electronic ignition with a start up ignition retard.
Then eliminate all advance in the distributer, lock it in at 34-36 degrees.

Retard to start, full advance for driving.

 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tached_out Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2018 at 10:54pm
Originally posted by WhatISit WhatISit wrote:

Yeah, I’m pretty much accepting at this point that the cam’s too much for my setup. I can make it work, but it’s still not going to be perfect, and it’s probably not going to have very good street manners.

According to the cam specs and the rest of my setup, Hughes gave me a 2500 RPM stall converter. I don’t know the details exactly, but I’m pretty sure the engine has 9:1 compression. I think comp cams could stand to update their information a little bit on the Thumpr. I’ve been reading everywhere that this cam is more aggressive than advertised. I could stand to have a 2800-3000 rpm converter and 10:1 CR.

We spent about two more hours today tuning the carb and setting the timing. Best we can manage is about 1100-1200 RPM in park, and 750-800 in gear.

What did you set the timing to?

Glenn
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Post Options Post Options   Thanks (0) Thanks(0)   Quote purple72Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: Mar/04/2018 at 2:21am
Originally posted by tached_out tached_out wrote:


999s were lockups used behind six cylinders.

998s were not. They were used behind 304s a heavy duty case version of the 904 with steel caged planetary sets and an extra high gear clutch disk.



Actually the first lock up transmission AMC used was the 1979 998 on the 304. The 6 cylinders with 904s didn't get lock ups until 1980 or 81. 82 is when they went to a lower 1st and 2nd gear because 82-83 Have 2.21 gears. Don't believe me? Look in the 79, 80, and 82 TSMs. I have all 3 and I took the time to look it up.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bernie70AMX Quote  Post ReplyReply Direct Link To This Post Posted: Mar/04/2018 at 4:50am
Do not know your heads but I would check valve lash first could be open. Just sounds like to me cam problems.  If lobe is gone ( like a small block chevy )  you are beating a dead horse and going nowhere. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Mar/04/2018 at 7:59am
It's simple, too much cam for the compression ratio in an automatic equipped car.

A butt load of initial timing may make it work.

It looks they are getting close.
Gremlin Dreams
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