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Over the Hill / No Revs.

Obtong

Jedi Hopeful
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Hello Again...

I've been having similar problems to Bret's MGB. MY 74 MGB goes really well on flat roads, but if I try to go up a modest incline I have a hard time getting the revs up (low power). This happens in 1st. If I'm lucky my MG will slowly chug along until I get to the top of the hill, the revs/power will increase and I'm off. There have been times when I've stalled, the ignition light has come on, and I have had to roll backwards onto the road below!

This is not an ideal situation.

All the emissions control items have been removed, I have a new coil, alternator, points, plugs (0.032) and wires. The dwell is set (60), and my timing is at 11 @ 1500. What else should I do?

BTW, my plugs do look somewhat sooty (not oily); the engine has been running a little rich.

Help!

Obtong
 

aeronca65t

Great Pumpkin
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Your car is at the cross-over year, but I'll assume it's a twin carb engine (single carb cars started to be delivered in late '74).

Since it's "desmogged", be sure you haven't mixed up the vacuum line to the distributor. Your initial timing is about right (I've read 13 degrees at 1500....yours is close to that). Be sure your timing is advancing fully when the car is revved up. When your car is revving to about 3000 RPM, your timing should be about 25 to 30 degrees BTDC......there's no mark for this on the front pully, but you can estimate it with a chalk mark and see if the timing is moving up as you rev the engine (using a strobe timing light). A plugged or misconnected vacuum line could cause a lack of advance (also, mechanical problems in the distrib could cause this).

Be sure you chokes are not stuck "on" (part-way) or your float level isn't set too high. Obvously, you need clean air filters and oil in the carb dampers.

One of the most common "rich mixture" problems is on post-75 cars that have been desmogged (single carb engines). These cars have an EGR valve, which is sort of a "controlled vacuum leak"; if the EGR valve is disabled, the car runs rich. I doubt your car was fitted with an EGR. Another common problem that saps power on single carb engines is a torn carb diaphram.

[ 03-11-2003: Message edited by: aeronca65t ]</p>
 

Gary Lloyd

Jedi Knight
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Does it pop or fart or anything like that?? If so, you are tooooooo lean!! Other than that, check where the vaccum lines come off!! Different distributers are designed for different vaccum!!
crazy.gif
cheers.gif
 
OP
Obtong

Obtong

Jedi Hopeful
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Thanks for helping me out with this folks. Here's some more info:

1. Twin SU carbs, 25D distributor (41085A / 1166)
2. Nope, no popping sounds on acceleration. It just hesitates before cutting out on hills.
3. The vacuum hose is connected to the intake manifold via where the "restrictor" (Moss# 373-855, page 81) is located. This is where it was when I bought the car. (Is this the right place)
4. Everything else on the intake manifold is plugged.
5. The timing does increase when the revs go up.
6. My MG DOES NOT have overdrive
7. 18V672Z engine

Boggles the mind, doesn't it!
Obtong.
 
OP
Obtong

Obtong

Jedi Hopeful
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Originally posted by Obtong:
[QB]Thanks for helping me out with this folks. Here's some more info:

1. Twin SU carbs, 25D distributor (41085A / 1166)
2. Nope, no popping sounds on acceleration. It just hesitates before cutting out on hills.
3. The vacuum hose is connected to the intake manifold via where the "restrictor" (Moss# 373-855, page 81) is located. This is where it was when I bought the car. (Is this the right place?)
4. Everything else on the intake manifold is plugged.
5. The timing does increase when the revs go up.
6. My MG DOES NOT have overdrive
7. 18V672Z engine

Boggles the mind, doesn't it!
Obtong.
 

Bret

Yoda
Offline
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Obtong:
Originally posted by Obtong:
[QB]Thanks for helping me out with this folks. Here's some more info:

<<Snip>>
3. The vacuum hose is connected to the intake manifold via where the "restrictor" (Moss# 373-855, page 81) is located. This is where it was when I bought the car. (Is this the right place?)
4. Everything else on the intake manifold is plugged.
<<SNIP>>
Obtong.
<hr></blockquote>

Something else to keep in mind when trying to trace down manifold leaks, is that you might have a leak in the manifold Gasket. The previous owner of my 78B took a few “shortcuts”, and used some silicone gasket maker (red stuff) to try and seal some leaks. I discovered this when I had to pull the Manifold to remove and replace the Catalytic converter on my car. Check out the attached pic?

Manifold14.jpg


Ugly isn’t it? I actually keep this hanging in my garage as a reminder of how easy things can go wrong when someone thinks they know what they are doing. Looking close at the picture – you can actually see where both the intake (vacuum) & exhaust gases was getting around this tired old gasket.

cheers.gif


Bret
 

aeronca65t

Great Pumpkin
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Bad intake manifold gasket is a good point on sidedraft engines (the manifold tends to "hang", causing gasket failure)....an easy way to check this is to start the engine and let it settle into a steady idle. Spray WD-40 (or similar) around the intake gasket (between the head and manifold).....if the engine has a vacuum leak, it'll suck the spray in and idle speed will go down (the spay won't hurt anything).

May cause poor running, but usually doesn't cause rich, sooty condition.

[ 03-12-2003: Message edited by: aeronca65t ]</p>
 

Bret

Yoda
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Great suggestion, but should you find that your manifold is leaking. Don’t do like my previous owner did and take shortcuts. Spend a couple of bucks and replace the manifold gasket. Likewise – I highly recommend that when you order your gasket, order one or two extras to have on hand just in case.

Also if you do have to remove the manifold, I suggest that you go ahead and re-new the front & rear lifter cover gaskets. I did and was pleasantly surprised at the difference in the reduced amount of the oil I now find in my drip pan at week’s end.
cheers.gif


Bret
 

clint

Senior Member
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This may sound silly to ask now, but is there a nest in your air cleaners? Or are the filters really dirty? Had a no power problem on my bike once, ran rich, burned up gas...and no power.. try the first gear uphill on a freeway running 5mph on the berm on a motorcycle. Anyway, turns out my air filter was dirty. New filter and it ran like a top. Never had a running problem before, just kinda came on.
I have seen nests in the cleaners cause the same problem.
Also, do you have a vacuum gauge? What readings do you have?
 
OP
Obtong

Obtong

Jedi Hopeful
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OK Folks, I replaced the air filters as they were looking a little grubby, and used a carb cleaner spray on the carbs. I noticed little difference in performance. One of the filter covers had a little soot on the inside. The intake manifolds showed no sign of leaking.

I had noticed that while cleaning around the carbs, the undersides were oily (clean oil, not dirty). I topped up the dampers with carb oil and my MGB is is now running better. Is it just a coincidence, or can a carb damper low on oil cause these kinds problems?

Obtong
 

Bruce74B

Jedi Knight
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Oh yea....that was probably the problem...if the oil in the dampner gets low or gunked and the piston sticks, you're gonna run rich...and on the twins, if only one is sticking, it make for a real rough run. I think you found your problem!
thumbsup.gif


Bruce
 
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