Performance question

[CBidzinski2010]

Hello all,

I have an 87 K20 with the 350 and sm465 combo. I just bought the truck and have replaced many things including the cap, rotor, plugs, and wires, due to it running like $41?. She runs pretty well now but I have noticed that when it gets to a certain rpm in the higher range (can't tell as I don't have an rpm gauge) the truck immediate takes off like a rocket from that point. I was thinking maybe the timing is off a little bit or the vacuum advance is stuck at the advanced position. Any ideas? I'm hoping someone reading this has experienced the same thing. I want to pick up a vacuum gauge this weekend but I am also unclear of where to mount it to on the intake manifold. Thanks for any insight everybody.

 

[brianhannon]

Possible fuel delivery issues? Does it still have the old Quadrajet carb?

 

[CBidzinski2010]

Possible fuel delivery issues? Does it still have the old Quadrajet carb?

It has the TBI set up. I think the distributor is supposed to be different than what's in it. I believe they had electronic advance on the TBI series but mine appears to just be mechanical

 

[brianhannon]

And as far as the vacuum gauge goes, just route the line to wherever your advance line would go. I think at idle manifold vacuum should run above 18 or 20 hg.. Personally I would first check to make sure you have a steady flow of fuel, just because that's easy to start with (no filter issues if you have one, no clogs in the TB injectors, etc) If that checks out move onto spark. Throw a timing light on it just to see where you're at. Pop the dist cap off and check to make sure the advance mechanism is operating properly

 

[rich weyand]

Something people have mentioned here before, and which is a bugger to diagnose.

There is a little piece of rubber vacuum hose an inch or two long that connects the <mumble, mumble> to the <whatchamacallit> on the back of the throttle body. This hose is almost never replaced during normal service, and if it splits due to age hardening over the last 28 years, you get issues.

Can anybody provide more detail on this? Otherwise I would suggest looking around on the back side of the throttle body for a small piece of rubber hose connecting back in there somewhere, and just replace it.

 

[CBidzinski2010]

Something people have mentioned here before, and which is a bugger to diagnose.

There is a little piece of rubber vacuum hose an inch or two long that connects the <mumble, mumble> to the <whatchamacallit> on the back of the throttle body. This hose is almost never replaced during normal service, and if it splits due to age hardening over the last 28 years, you get issues.

Can anybody provide more detail on this? Otherwise I would suggest looking around on the back side of the throttle body for a small piece of rubber hose connecting back in there somewhere, and just replace it.

Haha will do, if it does turn out that this may be the problem I will post it on here and let you know, the thing idles a little sporadically even after a new IACV and coolant temp sensor. I can't imagine it's a fuel issue as it runs well in the higher rpm range. Most times with fuel issues the system works at low end but can't keep up for the high end. I do have a pressure gauge and need to check it anyways. I really appreciate the input here though. Always helps having something to look for.

 

[Georgeb]

Where is your timing set? Spec is 0 but mine likes 10-12 much better. Also check for a smooth voltage swing from the tps.