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44mm jetting?
baja_01 - February 27th, 2014 at 06:32 PM

Hi All
Need some advise on my motor, 78x69(2007cc), 044 heads, w120 cam, 9.1 CR and 44mm HPMX carbs.
Motor starts fine but pops and backfires thru the carbs. Jetting is:150 mains,F11 emulsion, 200 airs, 50 Idles and 36mm vents.Any suggestions on where to start greatly appreciated.
BTW freshly built motor with all new parts. Can't even run in cam because of all the popping and carryon...........

Craig Torrens - February 27th, 2014 at 06:58 PM

PM sent re jetting :tu:

Oh and I think you mean 78x90.5, not 78x69 !

baja_01 - February 27th, 2014 at 07:38 PM

Bugger stuffed that up:dork:................PM received thanks........
Frustrating after nearly 12mths building this........Maybe do the EFI caper soon..

BiX - February 27th, 2014 at 08:24 PM

Are you sure the leads are on correctly and the timing is right? I think this would be more of an issue than jetting.

vwo60 - February 28th, 2014 at 02:21 PM

50 idles are a bit small try putting a set of 55's, check that you have no vacuum leaks also, here is a good site, takes the guess work out of it when you start off, gets you close but still will need a bit of adjustment.
http://www.aircooled.net/vw-carburetors-jetting-102/ 

baja_01 - March 4th, 2014 at 05:57 PM

Okay......found my set of 60 idle jets(some 55's coming). Runs without popping thru carbs just need to fix a couple of oil leaks now:mad:

baja_01 - April 23rd, 2014 at 05:00 PM

Hi All
Got my jetting set up as suggested by CT. Idles great seems to free rev smooth but when driving you go to accelerate and it coughs splutters then clears. Seems to help if you give it a big bootfull.Idle jetting still a bit off maybe?

Bizarre - April 23rd, 2014 at 05:31 PM

are you sure the carbs are synched (perfectly)

They are opening equally

Bogging like that on acceleration I found to be more one carb opening earlier than the other

baja_01 - April 23rd, 2014 at 05:56 PM

I set them up with the sync tool. I'll check it again as the idle is a little high too.

Bizarre - April 23rd, 2014 at 06:02 PM

Just make sure they open equally
They can be sync'd at rest but as you go to open, one may move before the other

If you have the hex bar - they can do this by having slop in the drop arms or the cams

Watch as you apply the slightest pressure on the cable connection

baja_01 - April 23rd, 2014 at 06:28 PM

No hex bar, I'm using a centrepull setup......

vwo60 - April 23rd, 2014 at 06:56 PM

What size chokes are you running and what is the cam. 36mm chokes might be to large, what are you looking for with the engine, were do you want to make the power and how do you drive.

fish26 - April 24th, 2014 at 10:37 PM

IMO 36mm venturi is too big, but if you choose to use them my set up would be 55 idle, 155 main, 180 air

Few things:

044 heads, std valves? ported? chamber work?

Intake manifolds? match ported to head and carb? gaskets?

Any intake or exhaust leaks?

44 HPMX, cleaned and set up or out of the box? fully synced?

baja_01 - April 28th, 2014 at 05:55 PM

Thanks for the replies
Motor was built to have a little more oomph than standard, not drag racing. Heads and manifolds just smoothed a little , nothing flash. 40mm 35mm valves if I remember correctly. I do have a set of 32mm vents that I can try?
When I get time I'll double check the float level and set them up from scratch...........