May sound like a stupid question but, took my bus for a rolling roll tune up yesterday and just noticed on the receipt today that they did the timing at 5DBTDC - it should be 7.5 and it was set at 7.5 before it went in. If I change the timing back to 7.5DBTDC would that have any effect on the tuning/setting up of the carbs that they did at all?
If they know what they are doing I would leave it? It would have been adjusted to suit your current engine condition. Assuming they adjusted everything else too, carbs , points , checked plugs etc. does it run better than before or not?
The max advance at 3k rpm is more important it should be 28-32 degrees. More normally with a 009 disti most folk have to set an idle advance to more than 7.5 to achieve at least 28 at 3k. So if you plan ro change it check the advance at 3k first.
Isn't the point of a rolling road tune up to optimise the timing? My bus gained 15 HP (or is that 15 cow powers) due the timing being massively retarded, when last on a rolling road. Drives like a different van now. I would leave well alone - the road operator should of swung the dizzy a few degrees each way until the optimal timing compromise was found. Timing is everything in tuning, in answer to your posts title. All to do with optimum burning of the carefully controlled fuel air mix ( also sorted on the rolling road), when the piston is at the best place in its cycle.
Your right but the optimal timing on an air cooled is not the best temperature Aircooled engines need a certain amount of retardation to run cool
Very true, which is why using a rolling road familiar with the way of the air cooled is a good plan. I second your idea of giving them a call.
Given them a call and if sounds like they set it to 5deg because 'that's the figure it states in their manuals' - think they must have a generic figure for vw campers which probably relates to 1 1600 type 1 engine as opposed to my 1700 type 4. They set it up on a rolling road which gave 55bhp at the flywheel (66 when new). They didn't powermap it before they started fiddling about so I have no before and after figures. doesn't really seem to drive much different to before I took it in but ticks over better and doesn't bang at idle like it used to - also noticeably better on fuel. The receipt says 'check ign timing 5 DEG @ idle 35 DEG max' but think they probably just pulled the max fig from the manual rather than tested it, but can;t be sure as I was with them the whole time. They said 'bring it back and we'll reset the timing' but 40 mile round trip & I cab easily do this myself but didn't want to do this if its gonna put the idle speed up as this is one of the reasons I took it to them ion the first place. garage is a carb/tuning specialist rather than a vw expert. Would it affect the power having the timing set at 5DBTDC instead of 7.5DBTDC? Thanks.
It depends more on the full advance figure. Changing from 5 to 7.5 will speed up the tickover a little, but you can always put it back if you're not happy. Also I'd check that they actually have set it to 5 before you do anything.
Funny you should say that Zed - I phoned them yesterday to ask if they had actually set the timing to 5 - they said that they had (invoice states check/adjust timing to 5 deg) - checked this morning - guess what - yep, still at 7.5 as set by me! Bloody liars.
