Hesitation at low revs when warm

[davesmith84]

Just make sure you set it before tdc and not after.

If your bus is the same as mine you'll have a dent on the pulley, it'll be on the ridge closet to you. Then you'll have a v notch on the back ridge to the right of the dent. This is 7.5 before And is what I've timed to. Vac lines disconnected and blocked.

I just need to re time to 28-30 degrees at 3500 vac lines disconnected and blocked. Idle timing should then rest at about 7.5 btdc.

 

[NellyM]

Thanks for that Dave.

My pulley is the type with the numbers on it so when TDC is lined up with the mark on the engine casing (i.e 12 o'clock) should I be setting the timing to 7.5 to the right of TDC (which it currently is) or 7.5 to the left?

I hope that makes sense!! :?

 

[davesmith84]

Hey Nelly, Yeah I get ya.

You're right, 7.5 to the right of the TDC line. This means when 7.5 BTDC is lined up with the case line, your TDC mark will be to the left of the case line. I hope that makes sense! Let me know how you get on and if it makes a difference.

 

[NellyM]

Thanks for that Dave.

My pulley is the type with the numbers on it so when TDC is lined up with the mark on the engine casing (i.e 12 o'clock) should I be setting the timing to 7.5 to the right of TDC (which it currently is) or 7.5 to the left?

I hope that makes sense!! :?

This may help...the pen tip shows my current setting

 

[davesmith84]

Yup looks good. Maybe a gnats bollock to the right though. You want to be bang in the middle of 5 and 10.

 

[NellyM]

New set of HT leads coming in today so I will update you later on my progress.

 

[matt-me]

Double check the full dizzy code you have on the old volks home website. They can vary alot. I had this recently on a 78 bug which had been changed from FI to carb. The dizzy whichhad been put on was for a type 4 engine (5 atdc), so was not suitable for the conversion. Changed dizzy for one to be timed at 7.5 BTDC and the hesitation has almost gone.

 

[davesmith84]

Yeah, like Tricky mentions in another thread, it's important to remember that the Old Volks site is in reference to US models only. If I followed the site I would be setting my dissy at 5 degrees ATDC which I imagine would make the engine run like crap if at all.

 

[NellyM]

New HT leads fitted and timing adjusted to 7.5 and still the same :evil:

Off to buy a new carb......

 

[Hampole]

I've just solved my hesitation problem. Like you I thought it was a leak but couldn't find it. I eventually did though! It was the dizzy vac diaphragm that had perished. Therefore the carb was able to pull air into through the vac port. Changed for a new one and no hesitation.

 

[davesmith84]

How did you diagnose that was the problem?

Shame to hear that Nelly. I honestly thought it would sort your issue out

 

[Hampole]

I took the vac pipe off the carb, kept the other end connected to the vac can on the dizzy, then I sucked on the pipe. You should not be able to draw any air. With mine, it was like sucking through a straw, so I knew the diaphragm had gone. With a working one, you should be able to see the plate the points are mounted on move inside the dizzy if you suck on the pipe. Just take the dizzy cap off and suck. If nothing moves, the plate is stuck, or if you draw air like I did then the vac diaphragm is perished. Either fault will cause poor bottom end performance.

 

[NellyM]

Thanks Hampole hadn't thought of that, I will check it in the morning.

 

[NellyM]

Timing set to 7.5 and new carb fitted and........no more flat spot :lol:

 

[davesmith84]

I'm resurrecting this thread as my hesitation is still present.

I went over everything again on the engine and it seems the vacuum can does have a leak. Sucking on it whilst on the vehicle I could see the plate move (albeit only a vey tiny amount) so I assume it was OK. Took it off the van and compared it to a new vac can and the different is night and day. The new one holds a vacuum where as the old one is like sucking on a straw. I got excited thinking this MUST be the problem.

So, I've swapped out my original bosch dizzy for a brand new Powerspark dizzy which I transferred my petronix over to. (I couldn't simply put the new can on the bosch as the alignment of the screw holes is different). This is the dizzy I now have on the engine:

http://www.simonbbc.com/distributor...ot-79-california-bus-bosch-points-distributor

After stating the engine, it seemed to sound much better. I let it warm up fully and I reset the timing to 7.5 BTDC, it was idling fine but if I pulled the throttle a little or a lot it wanted to stall. Something is definitely not right! I've also reset the carb according to the Bentley manual.

Bit stumped again! Any ideas?

 

[NellyM]

Hi Dave

I thought mine was cured with the new carb but after using it over a long distance I realised that the fault was still there. In the end I gave up and booked it in at T2D and as soon as I arrived one of there guys came out and asked me to start the engine again (still hot from a 30+ mile drive), he put his hands around the heater risers coming from the exhaust to the inlet manifold and said "there's your problem". One side was completely cold and the other was luke warm - they should both be hot. It is common for them to block from a build up of carbon from the exhaust and then the hesitation is caused from the carb icing up. New inlet manifold and 100's of mile later the fault is definitely cured!

I hope this helps.

 

[davesmith84]

You know what? That was exactly my next port of call! I'd say mine are warmish, one side more so than the other. I read that the manifold has to be warm to properly vaporise the fuel other wise it just 'pools' apparently!

Thank you so much for replying, I'll give it a go. It's engine out job, isn't?

 

[Trikky2]

It's engine out job, isn't?

No just an exhaust off normally. And old piece of clutch cable in a drill often does the trick.

 

[davesmith84]

Yes, I see, I can try cleaning it out with the engine in.

If it's really bad and I need to swap it for a new manifold, then it's an engine out job isn't it?

 

[Trikky2]

It's possible to change the manifold with the engine in the bus. Bit fiddly but do-able. Much easier with a twin port than a single port engine of course.