not quite running properly

[hotrodder13]

might have found the problem

on my 1 1/2 carb i think the piston inside is sticking could this cause the car to do what its doing, what happens is when i slightly put my foot down it goes and when i floor it it goes, but when i put the peddle half down the car jerks about, i am goin to put my bigger one , but could a sticking piston inside cause this problem

also how can you tell what the needle is

thanks tom

[bmcecosse]

Yes - a sticky piston will mess up the running no end! You undo the bell - lift it off with piston - needle is sticking out the bottom. Undo screw at side and pull needle out. the code is stamped on the side of the shank in little letters. Should be Axx form for a 1.5" SU.

[linearaudio]

Why, oh why are you adamant that you need a bigger carb?? You say it flies when you get revs up. A bigger carb won't improve on that!

A bigger carb will tend to make the engine response flatter at the bottom end which is exactly the opposite of what you are after.

Sort out your sticky piston, make sure your needle is something like, and enjoy the carb you have. If you are thinking of impressing people with the size of your carb, then adding "SU" to the description will take the edge off your kudos anyway:D

[hotrodder13]

not bothered about impressing people i just dont think its giving it giving my engine enought fuel, i cant get it to go faster then 85 (not on road )

[alainmoran]

bring it round and I'll take a shuftie at it ... it should be simple enough to work out if any of the common bits are broken (vac advance, dirty carb, bad float position, timing etc...) ... I don't know much about the race cam, but I can have a play with it and see what I can do.

[bmcecosse]

The size of the carb is not about fuel! It's about AIR. These are air engines - the more air going through, the more power it can develop. It's easy to add the correct amount of fuel!!

[hotrodder13]

well it has a k&n so i think its gettin enought air i can hear it sucking up, and i might bring it round but will have to be a sunday

[alainmoran]

I'm busy this sunday, but I think next weekend should be free.

Before you buy a new carb, I would start by cleaning the one you have - if the piston is not hitting the bottom with a clunk, then at low revs there is too much space between the bottom of the piston and the jet - meaning that there isn't enough suction to pull the fuel up from the jet. To compensate for this I would guess you have wound the jet out and made it run over-rich (hence it being thirsty), and no doubt you have then adjusted the timing to help compensate for it being over rich :s

I 'recently' went through something similar myself, and after lots of head scratching, carb & dizzy rebuilding etc.. I learned a lot about how the ignition/fuel system actually works - I knew the theory alright, but there's no substitute for taking things apart and seeing what's really going on in there, then sticking your hand in an turning the dizzy while it's running till you hit the sweet spot ... messing with the mixture until it runs right on the plunger test, sticking your hand back on the dizzy again (rinse, wash, repeat)

Have you read Vizard's book yet? He has a few things to say in there about over-carburation that you might want to read before sticking a set of DCOE's on there ;)

[bmcecosse]

Blimey - going straight to split Webers now!

[hotrodder13]

wouldnt mind twin webber but i aint got that kind of money

[hotrodder13]

found out what needle it says aac and the piston does move with a push

[linearaudio]

Piston should drop under its' own weight- something wrong if you need to push it!

[hotrodder13]

it seems ok entill i put the dash pot on

[bmcecosse]

Even with 3 in 1 oil in there - with the little damper removed - the piston should rise easily under one finger - and then drop with a 'clunk' . As you can see - the AAC needle is desperately weak - you should have AAA needle in there - but even that is just a starting point. Certainly that AAC is useless.[frame][/frame]

[hotrodder13]

well it drops witha clunk but dosnt rise, i might try get a new needle then

[hotrodder13]

WERE CAN I GET AN AAA NEEDLE CANT FIND ONE
also will running the engine to week damage it

thanks tom

[bmcecosse]

Burlen ? And yes - too weak can ruin the pistons. But i guess - if gentle with it - it should be ok for short trips. But you need to get that piston moving smoothly! Looks like Burlen may not have the AAA - best phone them!

[hotrodder13]

kk orderd one from mini spares what needle should be in a hif44, and im not gona drive it till i get the new needle in as i dont want to break this engine. and what can i do to get the piston moving

thanks tom

[bmcecosse]

BDL is a good starting point for an HIF 44. Can only clean/lightly polish the piston/bell assembly. Don't use anything more than T cut. But do check it with the damper removed...........

[hotrodder13]

can i ask which bit is the damper thanks and ill give it a wipe over 2moro