Really really bad Mpg

[thejinx]

Ok. I put 35 quid in the van and did 83 mile. Admittedly on a hilly place in the black mountains but surely there is something wrong. I worked it out to 12 MPG. Valves set timing set so what is wrong. Any help would be great as this will skint me otherwise cheers

 

[911gt2]

check your oil. Is there petrol in it?
Sounds like a leaky pump or line to me.

 

[thejinx]

Changed fuel pump not long back. But will check again. Would the plug gap have anything to do with this

 

[Moseley]

Nope, plug gap will make no difference to mpg - it'll only affect how well the fuel that enters the cylinder will burn and either give proper or reduced power output. Is it throwing out black smoke when you first start it and rev it? If fuel system is all intact, I'd be turning my attention to the carb setup. What is it and what engine spec are you running?


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[thejinx]

1600 TP. Solex 30/31 pict brand new and done less than 1000 miles. 009 electronic dizzy. Timing is bang on valve clearances done last week by myself. No smell of fuel in the oil. Also I rebuilt the top end and put new piston rings and scrapers in. Was wondering about compression now

Forgot to say. I get the odd backfire. Not all the time but now and again.

Today was pretty hilly

 

[user 20815]

How full of camping gear was your van? I'd start by getting a proper mpg reading. Fill your van full of petrol (and I mean full) do a nice round trip back to the same petrol station. Try and make it normal driving and try to make it a round number in miles (makes working it out easier ). Then fill your van with petrol again but this time see exactly what it used and then work out your mpg. I'd be surprised if it were only 12 unless you have a leak. Good luck.

 

[thejinx]

Yes worth a try. I had 4 adults and a few bits and pieces. A lot of up hill not much down.

 

[BRAD]

How about fuel pump pressure? It may be to high if your using a lot of fuel.

 

[thejinx]

How do I adjust? It seems a smaller pushrod

 

[Dave.P]

Fit a fuel pressure regulator (or filter king )after the pump, I always have since getting a silly pressure like 6-7 psi from my std pump.
I could be wrong but isn't a 34 pict3 the right carb for a 1600 tp?
Not sure how much less performance yours would give though ,if any..

Going over your other question about losing power up hills, don't all std engines do that (to a degree) ? Just how big are the hills and how slow is it going down to?
Had a slipping clutch years ago which was noticeable up hills but ok on the flat, just a thought.

 

[megaaircooledvw]

Wrong carb, wrong inlet manifold ,wrong dizzy

 

[dustrat]

Some 1600 cc TP were fitted with 30/31 Pict carbs but don't think that is your problem. Problem is 009 dizzy! Fit correct SVA distributor and will run as VW intended it to run.VW only ever fitted 009 dizzy to stationary engines. 009 dizzy is only ever any good if you are going to run at maximum revs all the time as there is no progressive advance.
Robert

 

[thejinx]

Ok. I am going to leave it for the rest of the year as I am not going anywhere and change back to my original SVA which is sat in the garage. I will do it at the same time as the lay up service

 

[weeboll]

009 v sva dissy wont make a difference in pulling up and down hills as you would always be working the engine hard up the revs and therefore at full advance. the vacuum advance only helps low in the range to advance the ignition ahead of the mechanical curve as I understand it

we got 25mpg full of gear, two kids one adult on a long drive to corfe and back in Dorset from High Wycombe this week, two weeks before we got only 21mpg on trip to norfolk because we spent a lot more time driving around locally rather than sitting on A roads.

on a motorway only trip I can get a heady 28mpg!

getting back to your problem

a leaky pump might squirt a litre or two max into the crank case but theres no more room after that so that doesn't explain it

backfiring on when coming off throttle is normal enough and no great worry, it doesn't take much fuel to backfire

so my money is on either a leaky hose which is a real worry, a mis reading fuel gauge or crap sums :lol:

 

[thejinx]

Checked hoses. All dry. I was also thinking crap sums so not overly worried at the moment.

 

[thejinx]

Removed fuel pump to find I had the wrong sized pushrod. A 108mm, changed to a 100mm and a new fuel pump so see if the issue gets better

 

[911gt2]

Removed fuel pump to find I had the wrong sized pushrod. A 108mm, changed to a 100mm and a new fuel pump so see if the issue gets better

Your pump wouldn't survive a wrong size pushrod. And even if it did the carb would regulate the fuel flow not the pump.

 

[thejinx]

Maybe true but I measured it and it was defo 108mm. I am running an alternator so it should be 100mm so unless the pump was also the wrong type I don't know. Now the pushrod and pump are correct for an alternator.

 

[purpledog07]

What carb did you have before and how did it perform?
What sort of fuel economy are you getting with an empty vehicle on a normal run?
Sounds like someone has done a lot of "improvements" to your motor over the years, like most old VW's!
Some history of what was replaced and when would be very useful.
Were all these changes done together or one at a time?
I'd be tempted to sort them all out and have it running reasonably. Do one thing at a time and see if it works before continuing. Have a good look at everything that could affect safety and performance.
Replace fuel hoses and breathers with 100% biofuel hose for safety if they haven't already been done.
A 34 PICT3 is the correct carb for your motor but it's hard to come across a decent one these days which is probably why you have the 30/31. This carb can perform OK on a twin port but check the jetting on the carb as they usually come jetted for smaller or single port beetle engines. If you are confident then do some research and experiment with different jets until you find the best result for you.
The 009 is well known to be a problem on any aircooled engine. How did you set the timing? The 009 requires different timing to the standard dizzy. I would
replace with the original vacuum dizzy as suggested, not forgetting the vacuum pipe to the carb. Unfortunately the electronic ignition is not likely to be a match so you may have to replace that as well or go back to points if you go down that route.

Nearly turned into an essay, there are so many things that can affect performance.

 

[thejinx]

Lines all done
Carb has the bigger jet
009 has been set at 28 BTDC
I have the original dizzy and my next move is to put it back on and bang the 009 on EBay. I understand the principle but can't remember where to put the vac advance hose on the carb. Going to leave it for when I do the service for the winter lay up.