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MG Midget and Sprite Technical - Good day at MGLive, spoilt by hesitation over 70

Hi folks, good day at MG Live on Sunday, 100 miles run up from the Isle of Wight. About half way up, at speeds over 70 mph the midget would hesitate, not serious enough to slow the pace much, first thought it was head winds.

The hesitation became rhythmic about every 10-15 seconds and I could not increase speed over 70. When slowed to 65, no problem.
On the way back problem returned, coupled with a hotter run (electric fan cut in for a while at 50mph, never happened before)

Tested the flow rate of the pump when cold at 1.25 pints per minute and no bubbles in the fuel.

Running an HIF44 on a titan manifold with a maniflow LCB. Electric fan with original removed.

Thinking its the pump/fuel line drawing in air, when hot and the increase in heat maybe lean mixture with air in the float chamber - what do you think?

Regards Tony
A Glynn

VOSA testing the new remote speed limit enforcement system?
David Smith

What does the tach do during the interuption

What kind of terrian does this occure....whindy turny hilly, or flat open road

Also how full Is the gas tank when this was occuring 1/2 or less ?

Did this only occure after the last Gas fill up, or has Iit been happening for several gas fill ups

Prop
Prop and the Blackhole Midget

Prop may have something there. Check the hoses for the petral. If they are real old replace them. They can collapse over time and impede flow. Is the engine stock? Are there any filters being obstructed. When the last time the distributor was servied? Just some things to look at!
Steven Devine

YOu can easily check the flow from the pump... disconnect one side of the coil (to stop sparks/engine starting), take the fuel pipe off the front carb, and switch on ignition. You should get a good slug of fuel every second or so. In terms of flow - it should fill a milk bottle in less than a minute... any bubbles means air is being drawn in.

BTW - if air was being drawn in, you might expect that the pump would tickety-tick every time you switch on the ignition, and keep going even when the float chambers are full (after 1/2 doz clicks...).

A
Anthony Cutler

Hi, thanks for you comments, in answer to Prop:

Rev. counter steady.
Flat/straight A road / motorway etc.
3/4 full tank to 1/4 full.
Only since the last fill-up (Morrisons supermarket, generally get all fuel from here)

Umm could this be fuel quality related?

Do Morrisons get rubbish fuel in their tanks for the Isle of Wight Music festival which was on this weekend?

Tony
A Glynn

Hi, had a look at the pump today, points black, worn right down and pitted - new SU on order.

Looking at the HIF44, before we left on Sunday, dashpot full, after the trip not a drop! and no damping whatsoever.

After 250 miles, where has the oil gone? can it be sucked out?

Confused Tony.
A Glynn

Gday Tony, gotta LOL, look at the other posts 'Dashpot oil vanished", seems no one can agree where its going, IMHO it evaporates. Nigel will be on soon chiding me for this, whatever, it does seem to disappear. I think it's a fuel supply problem for the original problem, expect the new pump should cure it. cheers
Rod
R W Bowers

Tony have you looked on the underside of the bonnet lately? I've seen the dashpot oil expelled through the tiny breather hole in the cap.
David Smith

Hi all, thanks for your responses.

New SU pumps are hard to come by at present, SU are waiting on springs before the next batch is available.

So cleaned and adjusted mine as a temp. measure - much stronger tick/tick with good earths and cleaned contacts - fuel flow fine.

Had a look at the HIF44, checked the float level, it was way out (far too low).

Also found the infamous third breather hole in the air filter back plate was covered by the gasket - cut a matching gasket hole, this made and car run lean, 1/2 turn richer and back to normal.

Anyone know where this hole goes, it sucks air in.

No obvious oil leaks from the dashpot, internally or externally - just disappeared after 250 miles!
Still a mystery?

Tony
A Glynn

I agree with David, easy to check too just clean that area on the underside of the bonnet and look for fresh oil

in the thread Rod mentioned I suggested, and do to you, to use 90 weight gear oil as recommended by John Twist - it wont cure any problem you have but helps with running

(Rod it wasn't me that chided you for that idea but I don't agree with it)

Nigel Atkins

Hi David & Nigel, there is no breather hole in my damper cap?

Tony
A Glynn

then the hole must be in the dashpot or elsewhere or you have the wrong cap

there's a John Twist video on this
Nigel Atkins

This thread was discussed between 17/06/2013 and 21/06/2013

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