Gravity fed carb, fit a pump?

Gravity fed carb, fit a pump?

Author
Discussion

oakdale

1,272 posts

169 months

Wednesday 9th June
quotequote all
One thing to bear in mind with this is that although it's only a small low powered engine, I'd imagine the mpg is pretty poor.
When going up hill with your foot to the floor, it's going to need a good flow of fuel.


Tyre Smoke

Original Poster:

17,725 posts

228 months

Wednesday 9th June
quotequote all
It does 35+mpg which I'm pleasantly surprised about. There is only one carb feeding two 300cc cylinders (595 total cc). 30hp.

Ambleton

5,287 posts

159 months

Thursday 10th June
quotequote all
Tyre Smoke said:
It does 35+mpg which I'm pleasantly surprised about. There is only one carb feeding two 300cc cylinders (595 total cc). 30hp.
That in itself isn't unusual, many motorbikes have single or multiple gravity fed carbs and much larger engines.

The throughput of fuel will be double that of a comparatively sized four stroke engine.

Im sure it's a combination of fuel hose and filters.

Here's one for you...

I'm not sure what the carb is like one these but have you checked the float level BTW? If it's a tiny fraction too low, and the main jet is forward of the float, then on the flat the fuel level in the bowl may be just about right for the main jet to pick it up. When going uphill, the fuel level in the bowl will go back, raising the float and limiting the fuel flow through the valve, meaning your main jet might not be sat in fuel and thus stuttering and low power.

Tyre Smoke

Original Poster:

17,725 posts

228 months

Thursday 10th June
quotequote all
Very valid point. The carb is brand new (well complete refurb) and was apparently all set up ready to bolt in and go. Which I did and she was a pig to start and doing 15mpg. Turns out the air correction screw was all the way in!

There are only three moving parts, the float, the butterfly and the choke. It wouldn't surprise me if the float tab was a bit out and shutting off supply uphill. However, fuel line first, remove in line filter and go from there.

Penelope Stopit

8,718 posts

76 months

Thursday 10th June
quotequote all
Been visiting back here to get the latest news, it's a goodun

How steep are the hills?

Tyre Smoke

Original Poster:

17,725 posts

228 months

Friday 11th June
quotequote all
It's Devon, not Lincolnshire. I'm going to have a rummage with the fuel lines this weekend and see if that makes a difference.

Baldchap

4,453 posts

59 months

Friday 11th June
quotequote all
I once added an in-line fuel filter to a GPZ500S that should have been fine in terms of flow rates, but caused it to cut out intermittently at higher throttle openings. Removed it and it was fine.

Ambleton

5,287 posts

159 months

Sunday 13th June
quotequote all
C'mon man. Its nearly 6pm on Sunday... you've had all weekend and still no update.

AW111

6,853 posts

100 months

Sunday 13th June
quotequote all
Ambleton said:
C'mon man. Its nearly 6pm on Sunday... you've had all weekend and still no update.
He's stuck in a valley somewhere - the only way out is uphill.

Tyre Smoke

Original Poster:

17,725 posts

228 months

Sunday 13th June
quotequote all
All good. In line filter out, not changed the pipework. Think I've fixed it with your help.

Ambleton

5,287 posts

159 months

Sunday 13th June
quotequote all
Hurrah! Best bet is always try and replicate as it came out of the factory as it worked then!

Sometimes we're too clever for our own good!