44mm jetting?

baja_01 Slammed & Awesome Dubber

84 posts · joined Jul 2009 · 27 Feb 2014, 6:32 pm

#984545

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 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 · 27 Feb 2014, 6:58 pm

#984553

PM sent re jetting 👍

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

baja_01 Slammed & Awesome Dubber

84 posts · joined Jul 2009 · 27 Feb 2014, 7:38 pm

#984558

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

BiX Veteran Volks Folk

2,499 posts · joined Sep 2002 · 27 Feb 2014, 8:24 pm

#984571

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

I have no sympathy for my car, only the wallet that pays for it!
Go hard or go home!!!!

vwo60 Veteran Volks Folk

2,036 posts · joined Feb 2007 · 28 Feb 2014, 2:21 pm

#984635

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 Slammed & Awesome Dubber

84 posts · joined Jul 2009 · 4 Mar 2014, 5:57 pm

#985050

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😠

baja_01 Slammed & Awesome Dubber

84 posts · joined Jul 2009 · 23 Apr 2014, 5:00 pm

#989235

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 Moderator The artist formerly known as blue74l

12,789 posts · joined Aug 2002 · 23 Apr 2014, 5:31 pm

#989237

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

Futue te ipsum!!!

baja_01 Slammed & Awesome Dubber

84 posts · joined Jul 2009 · 23 Apr 2014, 5:56 pm

#989238

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

Bizarre Moderator The artist formerly known as blue74l

12,789 posts · joined Aug 2002 · 23 Apr 2014, 6:02 pm

#989239

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

Futue te ipsum!!!

baja_01 Slammed & Awesome Dubber

84 posts · joined Jul 2009 · 23 Apr 2014, 6:28 pm

#989242

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

vwo60 Veteran Volks Folk

2,036 posts · joined Feb 2007 · 23 Apr 2014, 6:56 pm

#989243

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 Fahrvergnugen

903 posts · joined Jul 2007 · 24 Apr 2014, 10:37 pm

#989354

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?

bitten by the bug..........several times

baja_01 Slammed & Awesome Dubber

84 posts · joined Jul 2009 · 28 Apr 2014, 5:55 pm

#989659

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...........