I have a Chevy 250cid with a TBI system. I was changing the plugs today and decided to check the timing. I decided for a test run...

I forgot to connect the hose back to the can. I was told by Howell that the system needs the hose connected for advancement on timing.

What would happen if I stopped using the can/advancement? I only ask because it ran a whole lot better!!! What gives with that?

Chevytown

 

You lost me here. First off did you mean a 350 or 250? Secondly there is no "hose" for the timing unless you've got a vacuum advance dissy. If it's a stock TBI setup then it's electronic and you have to unhook the tan wire weather connector over on the passengers side to set initial timing. Once that is done, turn the car off and plug it back in, turn on and drive around. If you're talking about the wire and why it drove better with it unhooked then I don't really know why except that there is a backup plan in the dissy. For example; if the dissy doesn't get a signal from the ESC and it detects the motor spinning above a certain RPM it will advance the timing! It's kind of a backup plan just incase things go fubar with some wires. Oh yeah, and I don't know what you're talking about when you say "hose" and "can". What can are you talking about?

 

The 'can' would be the vacuum canister on the dissy. The 'hose' would be the vacuum hose.

Howell makes setups that use TBI, but don't really need everything to work like a stock unit. For instance..... a guy I know who put an LT1 in an '83 1/2 ton had Howell set up the ECM so that he didn't have to use any emissions, and he wasn't using a 4L60E.

The only reason I can think that it ran better with the dissy not hooked up is the base timing is set too high? Either that or if you have an adjustable vacuum can then you need to bring it down. If you don't have an adjustable one, then you may need one.

Those are the only two reasons I can think of that would make it run better with the vacuum advance not hooked up.

AJ

 

I can see someone understands what I'm talking about and the other is passin' gas...

Last night:
I just realized I forgot to mention that I put the timing marks(damper/timing tab) just about even. I don't have a tab, but rather a mark on my timing cover for TDC.

So with the timing marks being even and the hose not connected, there were two main things I noticed. The exhaust had a MUCH more aggressive note and overdrive actually kicked in when I put the pedal down, not like before, when it would kinda take a couple of seconds to kick in...

However, it wanted to turn off sometimes when I came to a stop. So I put the timing back near where it was before. I put a little less timing in it this time.

Today:
I noticed the stumbling stopped when at WOT on first gear. I only tried it once, so I'm hoping it wasn't a fluke. It felt smooth. Maybe it had too much timing to begin with.

Does the ECM "read" (for lack of a better term) the vacuum off the throttle body for advancement?

CHEVYTOWN and it is greatly appreciated hometown.

 

You were right on the money AJ! I'm gonna call ya "hound dog" homes!

The stumbling is gone. I just rolled around a bit and did 5--1st gear WOT runs (all getting on a freeway) and all were smooth. No mo stumbling! Looks like it had too much timing. I want to keep the can for better gas meilage. This modified L6 rocks now. Thanks for your insight hometown.

Chevytown and the GENERAL MOTORS GANG!

63 C10 stepside

 

Glad to see you got it running well but I still don't undertand why this is in the TBI board. You'de have gotten more insight if you had posted on the carb board. Usually when you're talking about TBI it comes with the computer controlled dissy. Might want to post over there for help tuning the vac advance can.
So is it a 350 or 250 and why did you go with the TBI for fuel only?