A little more pep for all of you Carburated folks Out there. Options

[pcdarks]

This is something for you to try to get more pep when you first hit the gas. First of all read it through until you understand what I did. I switched over from FI to a center mount progressive two barrel carb but this would work with any carb configuration. I had the stock distributor with vacuum advance and retard. I hooked up the vacuum retard to ported vacuum on the carb. What this does it retards the timing at idle. I then timed the engine with the vacuum hooked up to factory specs. The engine idles as it should at around TDC. As I start to accelerate from a stop the vacuum drops and the retard in the distributor releases giving me a little timing advance and the engine takes off with more pep. This advance works until the engine catches up and vacuum increases causing the distributor to retard to stock timing. Now the mechanical advance works for the rest of the acceleration. If I am cruising in a higher gear and give it gas the distributor again advances when the retard losses vacuum when the pedal is pushed giving the car mare advance again until the engine increases vacuum where it then retards to factory timing. At cruise speeds. the distributor mechanically advances to 27 degrees and runs there until again acceleration causes the vacuum to drop and momentarily advances the timing. The car has very noticeably better take off from a stop and accelerates quicker at speed. try it.

[PlaysWithCars]

Be sure and check your total advance. Its been too long since I worked on a -4 to remember exactly what the timing curve looked like. But, if I understand what you've done correctly, you are getting more advance at low speed acceleration which will make it peppier but you might also be getting excessive advance at high rpm WOT acceleration that could lead to pre-ignition. Check your total advance at 4000 rpm with the vacuum line disconnected.

[pcdarks]

Be sure and check your total advance. Its been too long since I worked on a -4 to remember exactly what the timing curve looked like. But, if I understand what you've done correctly, you are getting more advance at low speed acceleration which will make it peppier but you might also be getting excessive advance at high rpm WOT acceleration that could lead to pre-ignition. Check your total advance at 4000 rpm with the vacuum line disconnected.

Been there done that. The timing advances to 27 degrees at 3200rpm. If the pedal is floored at cruising speed it will momentarily advance it further but for so short of a time it will cause no problems. I stated this in the original post. Had you read it entirely you would have seen it.

[JamesM]

Been there done that. The timing advances to 27 degrees at 3200rpm. If the pedal is floored at cruising speed it will momentarily advance it further but for so short of a time it will cause no problems.

Assuming you are not actually verifying your timing while flooring it driving down the road... So what is happening here is the the minor load on your engine from accelerating it up to speed is enough to drop some vacuum and you lose the retard/timing over advances but once the RPM has stabilized it comes back down to 27. The problem is these are not the conditions you drive under and when you are actually under load while driving this is happening all the time.

Take a drive WOT up a long, steep grade on a hot day and report back...
PS. I have some spare motors sitting in my garage when you do.

Your timing is over advanced.

I've also noticed that the car runs better when it's still a little cold. No stumbling. Has anyone tried this?

Advancing timing can help with cold idle, its actually a feature that they have built into Megasquirt for that reason (and im sure other injection systems) only with Megasquirt it dials back the advance once the engine is warm so you dont damage your engine by running to much advance all the time.

KELTY360 is correct, your title is misleading, really you need to suck it up or you won't be making any friends here and if you're serious about the 914 you will need help here from time to time.
I'm an engine builder, I've been into building VW 's over 30 years, and into the 914 for 20 years...I still get things wrong about these cars all the time, but I suck it up, learn and move on.

Come on Mark, dont be so harsh! (IMG:style_emoticons/default/biggrin.gif)

Ill help out anyone regardless of whatever differing beliefs they may hold about life, the universe, and everything.... and carbs. Just as long as they don't piss me off, and to date only one person on this board has managed to relieve themselves of me ever offering my input on their threads again. And lets be honest at this point with all the information out there on the shortcomings of the single carb setup on these cars anyone who still swears by them I just view as sort of having a religious belief, and I learned a long time ago not to get into arguments over peoples beliefs. Personally never been a fan of praying the the controlled fuel leak on top of my motor is delivering something near the optimal amount of fuel as i drive down the road. Me, I'm an engineer, I like data, that's why I run a system that can log it all!

More than happy to share findings from that data if it helps get people on the right track!

(IMG:style_emoticons/default/beerchug.gif)


To your point though, I could see a car with dual carbs and a hot cam having an absolute trash vacuum signal that would throw the timing all over the place so yeah... probably wouldn't want to do something like that in that case... or at all, given the only thing going on here is over advanced timing.

[ChrisFoley]

Your timing is over advanced.

Adds a little more pep.

[914_teener]

Your timing is over advanced.

Adds a little more pep.

Just goes to show ya that belief systems are relative to the observer.

Someone says pep and someone says overadvanced timing.

Timing is relative ......and pep and overadvanced timing are entangled.

Starting to sound like Veeks now.

I'll rest my physics belief system and move on.

[JamesM]

Timing is relative ......and pep and overadvanced timing are entangled.

Right up until the rapid unscheduled de-tangling (IMG:style_emoticons/default/lol-2.gif)

But if he likes how it runs tuned that way than cool, who am I to say how to tune your engine. Im just saying his max advance under load is more than the 27 degrees he set it at unloaded and to much advance under load can have its downsides.

When I was much younger I one time mistook the 27 degree mark on my fan for meaning 0 and timed it using an adjustable light set at 27. Off idle response was amazing!!!

and now i know what to call those crackling sounds it was making...

PEP!!!!