Sounds like the ignition coil is failing. The key symptom is that it is worse when hot.

Ira

On Jun 18, 2022, at 7:04 PM, Kevin McLemore <kmclemore@...> wrote:



Yeah, I'm with Kenn. It sounds a lot like ignition, as we discussed earlier. I'd replace the distributor temporarily with an original points distributor and see how it runs... if it's good then you can either replace the Pertronix or go with original. There are plenty of good used dizzys around to use temporarily.

Cheers,

Kevin

---

From: PhillyMGClub@groups.io <PhillyMGClub@groups.io> on behalf of Kenn & Kathy Brown <oldmainlinehomes@...>
Sent: Saturday, June 18, 2022 6:55 PM
To: Philly Mg club <PhillyMGClub@groups.io>
Subject: Re: [PhillyMGClub] Suggestions on Troubleshooting

 

Hey Roger,

I had some symptoms similar to yours when I got my current B. It ended up being the electronic ignition. I refreshed it with a petronix and it worked well again.

YMMV...

Kenn 

Brown

 RS282284

CHRISTIE'S International Real Estate
Long & Foster Devon

   

On Sat, Jun 18, 2022, 6:36 PM Roger Searle via groups.io <searlerb=aol.com@groups.io> wrote:

All,

I wonder if you can provide some advice on troubleshooting a progressive issue with my 1978 MGB – sporadic engine hiccupping/roughness.

I think I mentioned before that over the last several years there is a sporadic engine hiccup.  Typically, this happened only when the engine is thoroughly warned up and when lugging the engine such as when coming out of a tight turn at low speed in too high a gear.  Now it’s happening quiet a lot and the engine has begun missing for several seconds when cruising at road speeds.

Background information

-          A couple weeks ago I drove a the rally on a warm day with a fair bit of stop-and-go traffic and experienced the hiccupping many times but no sustained roughness.

-          Today on cool temperatures, I went  50 miles with a mix of driving with hiccupping only a few times and one episode of roughness for several seconds while cruising (45 MPH).

-         I have electronic ignition, I think Petronix, about 15 years old – replaced when car restored around 2006 and engine rebuilt.

-         Sustained roughness feels similar to when one cylinder has a stuck valve (experienced this 25,000 miles ago right after engine rebuild).

-          New contactless fuel pump installed seven or eight years ago.

-          I typically use Sunoco Ultra 93 gas.

Troubling shooting so far.

-          Engine starts easily and runs smoothly when not hiccupping/missing.  Slight miss at idle.

-          At high speed (75+ MPH) and sustained full throttle runs smoothly so likely not fuel starvation.

-          Checked appearance of spark plugs.  All look good and alike with slight carboning and no oil.

-          Replaced leads from distributor to plugs and coil.  The old leads had resistances from 300 to 400 ohms,  The new ones 500 to 700 ohms.  Problem continues.

Any suggestions you can make on troubleshooting to isolate the problem will be appreciated.

Thanks,

Roger S.