No vaccum on one cylinder

[kbran]

I have little to no vaccum on one cylinder on the 86. It will not read on the carbtune, althou you can feel a little on the tube at manifold and if you take the restrictor out the rod will move up about an inch and bounce. I did a compression check this evening and all cylinders were around 200 plus or minus 4 lbs., which the manual says 199 is the high side with 142 being minumum and 171 standard. I have tried spraying WD40 around the carb boots with no rise in rpm. I checked the tube at manifold with a torch cleaning tip and felt no obstructions. All this was advice from Muffinman, Jeff I rechecked the compression on 1 and 2 only turning it over 3 times and the front cylinder read 150 and the rear 90lbs.

Any one else have any suggestions?????????

[93 venture]

One of Throttle plate stuck open more than the rest.

intake boot cracked.

check valve lash,might have a tight valve or burnt valve.

do a cylinder leak test.

[mtman]

Well kbran..

I know you don't want to hear all this "good news" but some way out there causes of low compression are:

Cracked cylinder head

Blown head gasket

Burned or warped exhaust valve, cracked guide, bad seal

Broken valve springs

Broken top compression rings, cracked pistons or scored cylinders.

Bad cam lobe or bad lifter.

I hope it's "E" none of the above but they had to be included as possibilities.

[wild hair 39]

do the valves,had the same thing happen on both the 89 & the 86,the 86 had 14 of the 16 valves were to tight,,89 only 1 valve was to tight,compression on that one was 70#,so i set them all at ,intake--.006 exh--.008,compression came back up to 170# to 190#

 

remenber to move all the carb over flow tubes,that makes the rear val cover easler to come off

 

:080402gudl_prv:

 

if you have time run up here,and i will help you,if i,m home

right now i,m fighting the blood pressure thingeeeee

[Redneck]

Is the cylinder in question firing? what does the spark plug look like? Have you changed the plug? If you rev the engine and let off the throttle does the vacuum come up? If it does is it steady or fluttering? It sounds like the butterfly is not closing , you have a vacuum leak (spray manifold with starting fluid) or you have a tight valve. You can also check for vacuum leak by spraying gas into each carb throat.

[CrazyHorse]

Make sure you dont have any fluid in the carbtune line I had this happen at the restrictor fitting and the carb tune would indicate no vacuum.

[Gearhead]

When you did your compression checks, did you open the throttle all the way while cranking? You should.

 

Jeremy

[kbran]

When you did your compression checks, did you open the throttle all the way while cranking? You should.

 

Jeremy

Yes, had the throttle open.

Is the cylinder in question firing? what does the spark plug look like? Have you changed the plug? If you rev the engine and let off the throttle does the vacuum come up? If it does is it steady or fluttering? It sounds like the butterfly is not closing , you have a vacuum leak (spray manifold with starting fluid) or you have a tight valve. You can also check for vacuum leak by spraying gas into each carb throat.

New plugs, wire and it is firing, had a nice brown color. Took the air filter off today and looked in and the butterflys were all closed.

do the valves,had the same thing happen on both the 89 & the 86,the 86 had 14 of the 16 valves were to tight,,89 only 1 valve was to tight,compression on that one was 70#,so i set them all at ,intake--.006 exh--.008,compression came back up to 170# to 190#

 

remenber to move all the carb over flow tubes,that makes the rear val cover easler to come off

 

:080402gudl_prv:

 

if you have time run up here,and i will help you,if i,m home

right now i,m fighting the blood pressure thingeeeee

Still want to check the valves. We will get together Lowell.

 

I did find the clamp on the no vac cylinder down over the bend where the carb boot is to the engine and moved it back up in the corect position and retightened. Put it back together and had a little vac. on that cylinder. So I kept playing with the adjustment screws on the sync and managed to get up to 12in. vac on the carbtune. Went back around each cylinder and checked idle adj. and resynced and this time got at 14in vac. Was able to get them all pretty even and when reved up they would all rise pretty much together. So maybe I have it now but it is still poping. Could be the can of seafoam in the tank and will be checking for exhaust leak or other vac leak soon. Any way it has rained here all day but I did manage to take it out for a few and it ran strong. For right now, just going to run it and see what happens.

Thanks for the input.