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914World.com _ 914World Garage _ 96MM Cylinder and Piston Install

Posted by: DanPMan Aug 7 2005, 06:40 PM

Just installed a 96MM piston and cylinder set into our 75 914-2.0. Fuel injection has been removed and replaced with a 32/26 DFV. Upon restart, there's a lot of backfiring both through the intake and exhaust. Runs like #$$#@%!!! with no power whatsoever. So far we've reset the carb per Weber initial set-up procedures and performed some initial timing. It idles, but hydrocarbons read at well over 8000 and the CO% was at 5 to 7%. So we're probably real rich. Probably should be rejetted...
Question.... when we installed the piston and cylinder sets, we also performed a valve seat rework (with a Neway by hand). All valves were verified to seat. Do you think the backfiring and no power condition is due to any other cause besides the carb and timing set-up?????

Posted by: bd1308 Aug 7 2005, 06:45 PM

check your dwell..my car did the same thing right before my point block wore down to zero and caused my engine to do all sorts of crazy stuff.....

Posted by: DanPMan Aug 7 2005, 06:55 PM

Will do! I didn't have my dwell meter or timing light with me when we were attempting (key word!) to time it the other day...

Posted by: bd1308 Aug 7 2005, 07:01 PM

what sucks is that i actually lost my nice digital dwell meter, which was also a multimeter.

sigh....

point gap should be close to .012....

Posted by: MattR Aug 7 2005, 07:03 PM

Did you set timing? You could be off. Loosen the distributor cap, start the car up, and rotate the distributor at idle to see if that changes anything. You should be rotating like 30-40 degrees each direction max.

Posted by: Al Meredith Aug 7 2005, 07:04 PM

My experience tells me that backfireing means lean mixture or exhaust leaks. I always rejet the idle jet (inside the brass screw on the upper side of the carb) with a "55" jet. I think they come jetted for a 1600CC VW

Posted by: seanery Aug 7 2005, 07:08 PM

what about the cam? You've got nice pic pistons, did you upgrade the cam? I think your carb is probably a wee bit tiny for this application, too. I'm sure other more experienced teeners will correct me if I'm wrong.

Posted by: bd1308 Aug 7 2005, 07:08 PM

backfire from carb=lean
backfire from exhaust=rich

running after being turned off=rich

Posted by: Jake Raby Aug 7 2005, 07:34 PM

Remove that carb

Grab the biggest hammer you can find.....

Beat the carb into a million pieces and throw it in the trash..

(this is to keep another soul from the same BS later)

Install a set of dual carbs, or go back with EFI.

The single Weber with its long runners and piss poor CFM rating will create all sorts of issues- I consider them absolutely untunable and throw them away weekly.

Making the engine larger has further increased the issues- the carb simply can't keep up with the engine.

All your symptoms of backfiring lead to running lean-

Working with that carb is like pissing into the wind, but I think I'd rather piss into the wind as install or work with one!

Posted by: bd1308 Aug 7 2005, 07:44 PM

i enjoy my single carb setup......i know another 9fourteener with one too.

it's good.

i'll pay shipping if you send those my way, jake.

Posted by: lapuwali Aug 7 2005, 08:37 PM

QUOTE (bd1308 @ Aug 7 2005, 05:08 PM)
backfire from carb=lean
backfire from exhaust=rich

running after being turned off=rich

running on is usually lean, actually.

backfires can also be caused by incorrect timing.

Posted by: bd1308 Aug 7 2005, 08:40 PM

i dont understand....

why would the system run-on without any fuel to run-on with.........

Posted by: Bleyseng Aug 7 2005, 09:19 PM

Takes Jakes,DD,Brads and everyone else and chuck that POS carb.

FI or duals are the way to go.

Posted by: SLITS Aug 7 2005, 09:21 PM

Ok budding M.E........hot spots in the cylinder head (preignition) from being to lean. If the engine still continues to turn, it still draws fuel and air 'cause a carb don't have no fuel cutoff.

Are the valves to tight also?

Posted by: Bleyseng Aug 7 2005, 09:24 PM

QUOTE (SLITS @ Aug 7 2005, 08:21 PM)

Are the valves to tight also?

Thats my bet!

Posted by: bd1308 Aug 7 2005, 09:49 PM

that was my other therory.

It just worked out both ways in my head.

Posted by: redshift Aug 7 2005, 10:00 PM

popping.. i&o... and..

Yeah, valves.. may even take a sweet spot adjustment, with a lil carb, and big... knockers?

M

Posted by: rhodyguy Aug 7 2005, 10:02 PM

that must be just about like a theory.

k

Posted by: V6914 Aug 7 2005, 10:59 PM

QUOTE (DanPMan @ Aug 7 2005, 04:40 PM)
Just installed a 96MM piston and cylinder set into our 75 914-2.0. Fuel injection has been removed and replaced with a 32/26 DFV. Upon restart, there's a lot of backfiring both through the intake and exhaust. Runs like #$$#@%!!! with no power whatsoever. So far we've reset the carb per Weber initial set-up procedures and performed some initial timing. It idles, but hydrocarbons read at well over 8000 and the CO% was at 5 to 7%. So we're probably real rich. Probably should be rejetted...
Question.... when we installed the piston and cylinder sets, we also performed a valve seat rework (with a Neway by hand). All valves were verified to seat. Do you think the backfiring and no power condition is due to any other cause besides the carb and timing set-up?????

You, have plug wires, mixed up.