Vac but no mechanical advance

[creationblue]

Had a session on the rollers today, found i was running a Van dissy with no mechanical advance, Jason @ Interpro had seen 2 previous with this set-up. I thought it ran well, but th dyno showed that only relying on the Vac is fine whilst accelerating but as the vacuum dies off under load at full throttle the advance goes too meaning your not making any power exactly when you need it most.

I dont have the dissy part number to hand but its physically shorter than normal, well worth checking yours.

Just

 

[Tofufi]

I dont have the dissy part number to hand but its physically shorter than normal, well worth checking yours.

Just

Those are the distributors fitted to singleport engines. The vac can dimensions are also different, and they are matched to different carbs.

 

[creationblue]

I dont have the dissy part number to hand but its physically shorter than normal, well worth checking yours.

Just

Those are the distributors fitted to singleport engines. The vac can dimensions are also different, and they are matched to different carbs.

Thats interesting, as there is an inherent problem with the lack of advance, i guess its fine on a standard set-up..........oh well its gone now :lol:

Thanks
Just

 

[Tofufi]

I believe the carburettors are/were different on singleport engines, I'm not totally sure

1600SP used a 31 pict carb, 1600TP a 34 pict 3, for example. But yes, you need to use the matching distributor for the carb

 

[Bookwus]

Hiya Guys,

Just for the record............

In both 69 and 70 (single port engines) the 30PICT3 carburetor was teamed up with the vacuum only advance 205T distributor.

In 1971 Volkswagen went with the dual port engine and changed out the carburetor to a 34PICT3 and mated that with a DVDA style distributor, the 205Q.

At least, that was the shape of things on this side of the pond.

 

[creationblue]

This is the number on the Dissy 113 905 205 T & 023137035

The fact is that it deffo doesnt work with 34ICTs :lol: , something that i was unaware of when I read about mech & vac advance distributors.

Just

 

[Tofufi]

This is the number on the Dissy 113 905 205 T & 023137035

The fact is that it deffo doesnt work with 34ICTs :lol: , something that i was unaware of when I read about mech & vac advance distributors.

Just

That is from a 1600SP, and like you say, vac only.

Twin carbs such as ICTs, Kadrons and DRLAs typically need the later vac/mech style

Glad you've got it sorted now, anyway 8)

 

[easy]

Some of the ones you are talikng about Just can be from a stationary engine for like a water pump etc. I had one on mine that got removed for the later style

 

[Trikky2]

The vac only dizzys are not particularly clever TBH.

Back in the "old days" we regularly used to replace them with the mech and vac advance dizzys for exactly the reasons highlighted by the OP.

Vac only (and mech only like the 009) were cheaper to make and saved a few bob but apart from that they basically had nothing else to reccomend them.

Basically the aircooled T1 engine works best if it has a max advance under load at high rpm of around 28 to 32 degrees advance. Under light throttle at higher rpm its good to have a few more degrees to give you the improved economy (hence the vac can) and of course the vac can also gives a blip of advance when pulling away, hence helping the driveability and reducing the chances of a flat spot.

 

[AxlFoley]

just had a read through this thread, i'm running a 1500 or 1600 Sp with a 009 dizzy, im guessing this is not getting the best for my engine?

The question is now, what dizzy do I need?

 

[creationblue]

just had a read through this thread, i'm running a 1500 or 1600 Sp with a 009 dizzy, im guessing this is not getting the best for my engine?

The question is now, what dizzy do I need?

Get your self a Vac & Mech dissy, for reasons pointed out above, the vac only was fine as it goes, but, of course, now I have far more drivability.....

Just

 

[creationblue]

Thanks guys for the input here, Jase pointed out Easy that it could have been an industrial dissy too, where running at 2000rpm all day the vac only would have been idea, and cheap as metioned above. Thats the great thing about all this, always something new to learn 8)

Just