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power drop with rough running - starts and idles??

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emjhansen Avatar
emjhansen Eric H
Winnipeg, Canada   CAN
my 1600 and I were just driving home and all of a sudden the power dropped and it started to run rough. of course I was in rush hour traffic so I couldn't just pull over. when I stopped the engine still idled and after I turned it off to get out and check there was no apparent issue. I have had a stuck float in the past but that's not what is happening this time. got back in and it started right up and up to 1500rpm all is ok and then that's it and it starts to run rough and sound like a diesel.
no loose wires - no gas spilling from the carbs and it idles a little lumpy but actually better than if its cold.
where should I start to trouble shoot?
thanks

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Rob Z Avatar
Rob Z Silver Member Rob Zucca
Camarillo, CA, USA   USA
1960 MG MGA
Just a guess, but check to see if both carbs are opening and that a throttle shaft clamp didn't come loose only allowing one to open. Also check that both Welch plugs are on the ends of the intake manifold. Check ignition also. See of all plugs are firing and maybe swap out the condenser for a known good one.
That you say it sounds like a diesel, check the timing and that the distributor didn't move.
I'm no expert, but that's where I'd start. Also do a search on the gurus site for your symptoms.
Good luck



"Time flies like an arrow......Fruit flies like a banana"

barneymg Avatar
barneymg Barney Gaylord
(Somewhere in USA), Pick one (or more), USA   USA
1958 MG MGA "MGA With An Attitude"
Sounds like fuel starvation. Check fuel flow at the hose before the rear carb. Should be a gusher, at least one pint per minute.



Barney Gaylord - 1958 MGA with an attitude - http://MGAguru.com - barneymg@mgaguru.com

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emjhansen Avatar
emjhansen Eric H
Winnipeg, Canada   CAN
I will pull off the line as soon as I have some help. not sure how quick I can get back and forth to the key and don't want to be splashing gas all over. (that's the optimistic thinking that its not the fuel supply)
it is the fuel line on the right side of the fitting? best way to remove? loosen clamp and then back out off the banjo y union?
thanks for help.


Attachments:
carb picture for help.jpg    53.8 KB
carb picture for help.jpg

Rob Z Avatar
Rob Z Silver Member Rob Zucca
Camarillo, CA, USA   USA
1960 MG MGA
Yep. Fuel from tank on the right. Loosen hose clamp and pull it off the banjo. You could find some sort of container to wedge in there and stick the hose in it. Plastic soda bottle or something. You should have enough time to turn the key on and off that way. Should pump as Barney says, but it's only 1.5 psi or so.



"Time flies like an arrow......Fruit flies like a banana"

emjhansen Avatar
emjhansen Eric H
Winnipeg, Canada   CAN
ok - turned on the ignition and 5 sec give or take it pumped a couple of ounces of gas. is that what I'm looking for.
it didn't come out fast enough to splash off the bottom of the container but it was a steady stream.

barneymg Avatar
barneymg Barney Gaylord
(Somewhere in USA), Pick one (or more), USA   USA
1958 MG MGA "MGA With An Attitude"
Yeah, that's it. Sounds like enough fuel flow.



Barney Gaylord - 1958 MGA with an attitude - http://MGAguru.com - barneymg@mgaguru.com

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Blueosprey90 Avatar
Blueosprey90 Jeff Sienkiewicz
New Milford, CT, USA   USA
It could be a bad rotor, cracked distributor cap, bad condenser, corrosion on the plug wires - distributor end, bad coil. Your choice. Good luck. eye rolling smiley

emjhansen Avatar
emjhansen Eric H
Winnipeg, Canada   CAN
thanks Jeff - I will be checking all that out next. I will check that out and post some pictures of what I see. Is it likely those type of problems just manifest themselves like that? And even when the power dropped there was no accompanying noise ( that I could hear over the regular road sounds)
ps - I really enjoyed watching your racing videos!.

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Blueosprey90 Avatar
Blueosprey90 Jeff Sienkiewicz
New Milford, CT, USA   USA
Power drop and rough running may mean that you're running on less than 4 cylinders.

Start the car and let it warm up a bit. Then start pulling plug wires to see if loss of the spark to the particular cylinder affects how the engine runs. To confirm you have strong spark, pull the plugs one at a time, hook them up to the plug wire and ground plug on the block while engine is running.

My recent loss of power was attributable to corrosion in the sockets where the plug wires are inserted. At the Lime Rock Historic Festival, my first practice / qualifying run did not go well. Could only get up to about 4,000 rpm on wide open throttle.

After checking compression, valve lash and adjusting timing, car sounded good, but not quite right at the exhaust and an intermittent backfire when starting. Passerby said I had a misfire. I swore he was crazy, but pulled plugs. #2 was wet. Guy in the next space said I had a misfire. I swore he was crazy. Started engine and started pulling plugs. Pulling #2 and #3 had no impact on rpms. Seems I was running on just #1 and #4.

Pulled the distributor cap and it was dirty inside, but no smoking gun. Checked rotor, appeared OK. Pulled the plug wires. Corrosion visible in the cap where the wires plug in. Pulled out a used, spare cap and substituted. Motor seemed to be running on all 4 cylinders, although #2 and #3 seemed weak compared to #1 and #4 when pulling plug wires. Grounded plugs #2 and #3 on the block and they seemed to have a strong spark.

If you can't trace after all else, suspect condenser. But I think the condenser symptom would be more of a spitting misfire, inconsistent across the plugs.

dbradley Avatar
dbradley Dan Bradley
Winston-Salem, NC, USA   USA
My car has done this, very infrequently, since I've owned it, 20 years. Tooling down the highway buzzing like a bee and suddenly brappabappabrapbapbapbap. Learned to just get off the gas for a few seconds and it would come back. Replaced the Weber that was on it when I bought it with rebuilt SUs. Same issue. Put a Mallory dizzy on it for a while. Same issue. New fuel pump. Same issue. Guy on another board suggested maybe some crap in the tank floating up to the pickup. I've always meant to take down the tank and really clean it out, haven't gotten around to it. Some have said "water in the gas", but I doubt it.



Dan Bradley

'57 MGA 1500 Roadster
'38 Buick Special Coupe

Gary E Avatar
Gary E Silver Member Gary Edwards
Kernersville, ,N.C., USA   USA
I had a intermittent problem a few years ago and found my tank sealer was breaking down and plugging the pump Got an new tank and couldn't even give the old one away.



Gary

Blueosprey90 Avatar
Blueosprey90 Jeff Sienkiewicz
New Milford, CT, USA   USA
We had something like Dan's problem on my old engine. I figured fuel starvation because it only happened over 5,000 rpms, and if we lifted and coasted for a about10 seconds, power came back. It turned out to be sticking valves. angry smiley

copernicus Avatar
copernicus Nick Kopernik
Redding, CT, USA   USA
In reply to # 3591410 by Gary E I had a intermittent problem a few years ago and found my tank sealer was breaking down and plugging the pump Got an new tank and couldn't even give the old one away.

It wasn't sealer in my case, but those little plastic seals you find on the ends of a variety of types of additives. Car would run well and then die; wait a bit and the car would start up and run well, all day or for a week or so, until it died again. I went thru all of the usual suspects and then finally pulled the tank. Sloshed fuel around in it and then emptied it; one of those plastic seals came out. Sloshed it again and found some more. All told I think I found about 5 of them plus some other residue that looked like the remains of filters from a cigarette. Seems these items would float around until they got within proximity of the fuel pickup line in the tank & then they'd get stuck due to the pump's action, but then get released when the power was turned off. They never actually got into the line because they were too large, but they non-the-less stopped the flow of fuel.

dbradley Avatar
dbradley Dan Bradley
Winston-Salem, NC, USA   USA
Jeff's comment reminds me of another idea I chased, buddy of mine who rides motorcycles said "valve float". (Me: Huh? What's that?) So I put in "heavy duty" valve springs from somewhere, Moss or VB, with high hopes. Same issue. Now that I've gotten the car driveable for the first time in years, this might start biting me again enough to finally see if I can find any of Nick's cigarette butts in the tank. :-)

Just last week, thought I was having a recurrence, but it was just out of gas. Gauge never has worked (another of those things I'm going to do something about some day), go by mileage, but when I'm fiddling with carbs and timing and so forth in the garage, of course burn gas without going anywhere. Not the first time, what does it mean when you keep making the same dumb mistake?



Dan Bradley

'57 MGA 1500 Roadster
'38 Buick Special Coupe

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