HT Leads query HELP!!

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HT Leads query HELP!!

Postby hammy01 » Tue Jun 21, 2011 3:57 pm

Hi, my 1500 1975 Midget when setup on standard, 1.3.4.2. it will run rough it revs kept high but only fires on 1 and 4, i can disconnect 2 and 3 with no effect.
If i swap over 2 and 3 making it 1.2.4.3 it will run and is drivable but wont idle evenly it hunts and stutters. points ok, tappets ok, timing with strobe ok.
Suggestions please ?? forgot to say i have a good spark at all leads checked with those transparent in line checkers.
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Re: HT Leads query HELP!!

Postby Charlie Tolman » Wed Jun 22, 2011 1:26 am

The 1500 has a firing order of 1-3-4-2, and the distributor rotor rotates in a counter- (anti-) clockwise direction. If the rotor rotation is assumed to be clockwise, cylinders 1 and 4 will still have spark at the correct time, while 2 and 3 will not.

The idle issue with hunting and stuttering is a separate problem.
Look for vacuum leaks, and the engine might need a richer fuel/air mixture ?

Charlie T.
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Re: HT Leads query HELP!!

Postby hammy01 » Wed Jun 22, 2011 3:24 pm

How right you are, i was looking clockwise :roll:
I have a feeling it must be vacuum leaks as the carbs have been overhauled by a local garage recommended by local MG owners club.
although he had me replace the s/s twin pipe exhaust with a standard and it made no difference.

Is there a way to check vacuum ?

Many thanks

Iain
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Re: HT Leads query HELP!!

Postby hoggie » Wed Jun 22, 2011 11:35 pm

with the engine idling, spray some starting fluid at suspect leak points on the intake manifold. The engine will speed up slightly if it picks up the starting fluid from a leak.
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Re: HT Leads query HELP!!

Postby Charlie Tolman » Thu Jun 23, 2011 12:40 am

Please see my recent posting in the General section,
under Hunting at Idle, regarding vacuum.

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Re: HT Leads query HELP!!

Postby hammy01 » Thu Jun 23, 2011 3:22 am

many thanks for your help on this Charlie/Mike,
can you say, i have an old Crypton Econometer vacuum guage i intend fitting to the car, could i attach that temporarily to the distributor vacuum advance to get a reading?
I did try it but there was no reading at tickover but it did jump to about 25 on acceleration then dropped back to 0 on tickover. I am hoping this is the type that does not have a vacuum on the dist at tickover or i am in for some serious work.

Thanks again Iain
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Re: HT Leads query HELP!!

Postby hammy01 » Thu Jun 23, 2011 6:00 pm

just had another thought, if the breather pipe to the rocker cover and the cover itself were leaking would this cause rough running?
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Re: HT Leads query HELP!!

Postby Charlie Tolman » Thu Jun 23, 2011 11:56 pm

The vacuum readings vs. throttle position seem to be backwards.
Look at examples 1 and 2 in the link below.

http://www.earlycuda.org/tech/vacuum2.htm

Your vacuum line is on which "side" of the carb throttle plates ?

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Re: HT Leads query HELP!!

Postby hammy01 » Tue Jun 28, 2011 9:47 am

Hi Charlie,

it looks like its on the carb side of the plates.

could i tap into the breather pipe?
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Re: HT Leads query HELP!!

Postby Charlie Tolman » Fri Jul 01, 2011 12:45 am

I am not very familiar with the 1500 engine, but I would assume that the vacuum canister on the distributor would advance the spark timing with high vacuum at the intake manifold. This would occur at engine idle, and also when cruising along at a moderate speed.

The vacuum line from the distributor probably connects to a fitting on the intake manifold, or to a fitting on the carburetor that is close to the intake manifold (on the engine side of the butterfly valve).

Perhaps readers of this forum, who are knowledgeable on the 1500 engine, will comment on your vacuum readings posted earlier.

Charlie T.

P.S.: The breather pipe is not a good source of vacuum.
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