MGB will not go above 2000 rpm in any gear! : MGB & GT Forum : MG Experience Forums : The MG Experience

Re: MGB will not go above 2000 rpm in any gear! #21
JoeReed Joe Reed Cordova, Tennessee, USA 1978 MG MGB "Kermit" 1997 Jaguar XJ6 (X300)	Posted: March 29, 2012 08:58AM Registered: 7 years ago Posts: 8,782

I betting on the brake booster as well. You shouldn't hear ANY hiss from it - much less a LOUD hiss...

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Re: MGB will not go above 2000 rpm in any gear! #22
Sinewave T. Keith Vezina Kenner, LA, USA	Posted: March 29, 2012 09:24AM Registered: 7 years ago Posts: 1,236

Jon,
I'll bet your '79 California car has a single Zenith-Stromberg, not an SU. Besides all of the other good advice, check the oil level in the top of the carb and carefully inspect the diaphragm for tears. If you have to replace it, just note that there are locating tabs on both the inside and outside diameters of the diaphragm.

T. Keith Vezina
British Motoring Club New Orleans
1976 MGB, 1976 MGB Trailer & 1967 MGB MK. I

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Re: MGB will not go above 2000 rpm in any gear! #23
Boris67MGB Richard Boris Kings Park. NY 11754, USA 1967 MG MGB	Posted: March 29, 2012 10:33AM Registered: 3 years ago Posts: 272

I had a similar issue a few years back; replaced points, rotor and condenser and problem was resolved.

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Re: MGB will not go above 2000 rpm in any gear! #24
kuz1 Keith Kuzma Prattville,Alabama, USA 1971 MG MGB 1980 MG MGB Limited Edition (LE)	Posted: March 29, 2012 10:56AM Registered: 5 years ago Posts: 2,887

I'll bet points won't stop the LOUD hissing noise.

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Re: MGB will not go above 2000 rpm in any gear! #25
glbishop Gary Bishop Nashua, NH, USA 1980 MG MGB MkIV	Posted: March 29, 2012 11:56AM Registered: 1 year ago Posts: 545

Loud hissing at idle could indicate a manifold source vacuum leak but if that was the case it would idle too fast.

If it was a ported vacuum source leaking then it might make a little sound at idle, without raising the idle speed, and be a major leak when you open the throttle.

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Re: MGB will not go above 2000 rpm in any gear! #26
rossvesq Ross V Arlington, Virginia, USA 1967 MG MGB GT "Luigi"	Posted: March 29, 2012 12:05PM Registered: 1 year ago Posts: 251

In reply to # 2025354 by DB Wood Does the car still have a catalytic converter? When they fail, the ceramic catalyst comes apart and plugs the pipe up. Sometimes it dumps its guts into the muffler and plugs that up. This creates excessive back pressure and the car won't rev. A friend of mine just went through this with his daughter's 80's something Volvo.

FWIW, if AFTER you check all of the elec/fuel/vacuum/boosters/price of tea in china suggestions above and it's STILL doing this, I would concur with DB that exhaust restriction is probable. I've suffered same fate, and a simple way to check would be to unbolt the down pipe from the manifold and fire her up. Yeah, it'll be loud, but if it revs above 2K, then you found your problem.

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Re: MGB will not go above 2000 rpm in any gear! #27
glbishop Gary Bishop Nashua, NH, USA 1980 MG MGB MkIV	Posted: March 29, 2012 12:21PM Registered: 1 year ago Posts: 545

Many have suggested exhaust blockage.

Maybe the HISS is from exhaust blockage.

I've never had a cat plugged or muffler collapsed to cause that big of a restriction but I'm sure it happens.

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Re: MGB will not go above 2000 rpm in any gear! #28
biglawndog Scott Thomas Coconut Creek, Fl, USA 1979 MG MGB	Posted: March 29, 2012 12:23PM Registered: 6 years ago Posts: 143

In reply to # 2025708 by rossvesq

In reply to # 2025354 by DB Wood Does the car still have a catalytic converter? When they fail, the ceramic catalyst comes apart and plugs the pipe up. Sometimes it dumps its guts into the muffler and plugs that up. This creates excessive back pressure and the car won't rev. A friend of mine just went through this with his daughter's 80's something Volvo.

FWIW, if AFTER you check all of the elec/fuel/vacuum/boosters/price of tea in china suggestions above and it's STILL doing this, I would concur with DB that exhaust restriction is probable. I've suffered same fate, and a simple way to check would be to unbolt the down pipe from the manifold and fire her up. Yeah, it'll be loud, but if it revs above 2K, then you found your problem.

A further thinking a stopped up exhaust would act exactly like yours is acting. The cat could have collapsed. A easy way to check is to have someone rev up the engine and you go to the tailpipe and feel with your hand the amount of exhaust coming out.

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Re: MGB will not go above 2000 rpm in any gear! #29
biglawndog Scott Thomas Coconut Creek, Fl, USA 1979 MG MGB	Posted: March 29, 2012 12:38PM Registered: 6 years ago Posts: 143

In reply to # 2025719 by glbishop Many have suggested exhaust blockage.

Maybe the HISS is from exhaust blockage.

I've never had a cat plugged or muffler collapsed to cause that big of a restriction but I'm sure it happens.

I have had it happen in smaller engines and this is just how they acted. The early to mid 2000's Nissan Altima is known to have it's cat collapse and cause engine failures, fortunately I haven't experienced it.

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Re: MGB will not go above 2000 rpm in any gear! #30
spikemichael Michael Caputo Athol, MA, USA 1973 MG MGB 1973 MG MGB "Freebie" 1976 MG MGB "B-4" 1979 MG MGB "MegaBeanie" 1989 Suzuki Intruder 800 → more	Posted: March 29, 2012 03:39PM Registered: 4 years ago Posts: 6,923

I want to know what the hiss is before you spend any more money.
pull and plug the brake servo hose at the manifold not at the servo.

No hiss?

Put the hose on, plug it at the servo end.

Hiss? bad hose

No Hiss?

Put it back on the servo...

Hiss? Bad servo.

No Hiss? Hose wasn't on securely.

Michael J. Caputo
'79 RBB and '73 CBB owner with extensive experience in 12v Audio System design and installation.
Vendor of Regalia and Promotional Products. Forum Member with a warped sense of humor.

How to advertise on this website

MG CALENDARS! MGB or MGA order TODAY! – Athol, MA USA $20 delivered anywhere! Visit www.mgbcalendar.com or CALL 617-674-4367

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Re: MGB will not go above 2000 rpm in any gear! #31
mgbgreen Jonathan G California, USA	Posted: March 29, 2012 11:04PM Registered: 1 year ago Posts: 12

HI guys!

I was out all day, and didn't do much - but I DID replace the coil - absolutely no difference - rev it to 2000 and suffocates away again, foot off gas it stumbles along at around 500 rpm a few seconds then comes back to a good idle.

I took the hose to the brake booster off and plugged it - same as before... Plugged it back in to the booster - still getting some hiss, not quite as bad as before - it might be at the plastic lead nipple - but whatever I still got some boost, and that's not what's doing this.

More info on the car: - I have a crane xr700 ignition, so no condenser. Pulled all the plugs and all of them clean, no oil, and lightly hazed with white powder - they've been in about a year. Also, Keith above is right, I do have a zenith stromberg single carb (checked the Haynes again), and totally disassembling it is what I'm going to do tomorrow, and hope I can get it put back right smiling smiley

I remembered today that about an hour before I found the original fuel pump was just about dead and giving no gas, I had topped off the dashpot for the first time in about 3-4 months at least (trying any damn thing I could think of...). It has always leaked, that's why I had bought a diaphragm for it years ago, but then never did it. I could have fixed the 'stalling out completely' problem with the fuel pump, but maybe all that dashpot oil drained straight down into the carb somehow or something, or something...

Chasing gremlins... Close one door to keep em out and leave one open for them to jump right into.

I'm hoping it's the carbs. New catalytic converter is about $300 shipped, and who knows if it did blow its insides on into the mufflers... Today, running around the block, it did it's first set of backfires that it has ever done - which I've read online is other evidence of a bad cat...

Never gotten into a carb before, so any noob advice would be appreciated about what I'm getting into!

Anyway - thanks for all the advice so far! Keep it coming if you've got ideas.

Jon

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Re: MGB will not go above 2000 rpm in any gear! #32
Bankerdanny Daniel Palmer Chicagoland, USA 1972 MG MGB GT "Dudley" 1977 Honda MC Gold Wing	Posted: March 29, 2012 11:14PM Registered: 1 year ago Posts: 1,058

If your plugs are white that would indicate a lean condition, which would make sense if you are getting starved for fuel above 2k.

Personally I wonder if you still have an issue with the fuel pump. I know you did some work on it, but it still might not be pumping properly so you get enough fuel for low speed work, but not enough for over 2k.

By all means check the carb, if it hasn't been cleaned in the past 34 years it is probably due. But if that doesn't help I would spend the $60 for the Facet pump from NAPA (Moss sells the same one, but for $20 more) and try a new fuel pump. I have one in my car, it was an easy install and works very well.

Endeavor to Persevere

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Re: MGB will not go above 2000 rpm in any gear! #33
glbishop Gary Bishop Nashua, NH, USA 1980 MG MGB MkIV	Posted: March 30, 2012 05:57AM Registered: 1 year ago Posts: 545

In reply to # 2026338 by mgbgreen

I'm hoping it's the carbs. New catalytic converter is about $300 shipped, and who knows if it did blow its insides on into the mufflers... Today, running around the block, it did it's first set of backfires that it has ever done - which I've read online is other evidence of a bad cat...

Start by removing just the 4 screws on top of the carb. Lift off the cover and remove the air valve/slide. You can tap around the edge with a screw driver handle as you pull up on the cover to break it loose. The rim of the rubber diaphragm can be coaxed from its groove with the tip of your fingers. Don't just yank it off. Once you've done it it's literally a 1 minute job.

You will find out if the slide is stuck or if the diaphragm is torn.

As for the Cat. Don't spend a dime on a new one. Many on this site have stated that a hollowed Cat will pass the CA emission test. If you need I have one that is already hollowed out.

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Re: MGB will not go above 2000 rpm in any gear! #34
GILMGA Gil Dupre Chattanooga, TN, USA 1962 MG MGA 1974 MG MGB GT	Posted: March 30, 2012 08:48AM Registered: 6 years ago Posts: 7,333

I had this happen once and it was the inner wall of the exhaust pipe. When you floor the accelerator the exhaust whistles or doesnt exhaust much.

Gil

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Re: MGB will not go above 2000 rpm in any gear! #35
BumbleB74 William Milholen Tidewater VA, USA	Posted: March 30, 2012 09:55AM Registered: 7 years ago Posts: 4,685

If it is the CAT, you might be able to find a local shop that can hook up a generic one.....but maybe not, given how that thing mounts.

If you lived in another state, you might be able to just ditch the thing.

1974-1/2 Roadster, "Bumble Bee", Corvette Yellow - in shambles, wire wheels
1976 Roadster, un-named, Sandglow - "driver" condition (stock + 32/36 Weber DGEV, cast iron header, 25D distributor), bolt on wheels

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Re: MGB will not go above 2000 rpm in any gear! #36
mgbgreen Jonathan G California, USA	Posted: March 30, 2012 07:22PM Registered: 1 year ago Posts: 12

Hey guys

I have not made much progress today, as the PO seems to have secured the top cover of my carb with flat slotted ones that are not only frozen on but totally stripped.

But I have another symptom to report, that I don't know exactly what to make of. Could this be a sign of too much pressure building up in the exhaust, and it's likely the cat?

With the air cleaner removed, I was idling the car and decided to rev it up a bit, just to watch the action of the needle mechanism.

It started to backfire OUT of the carb, leaving black sooty grime inside the carb. I do not believe this is at all normal, right? Does it mean that it was ignited in the manifold, or in the carb itself? Or is it coming back out of the valves, because the explosion had no where to go out the exhaust?

I wasn't watching the tach, I was under the hood, but it couldn't have been going more than 1500 rpm - I had just barely nursed it up, and it did it several times.

Starting to think I need to take the advice of several people above and try and get that cat off and see if there is a difference.

Jon

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Re: MGB will not go above 2000 rpm in any gear! #37
mgbgreen Jonathan G California, USA	Posted: March 30, 2012 08:45PM Registered: 1 year ago Posts: 12

SOLVED!!!!!!!

Thanks for everyone's input. Several people hit it right on the head, but it could have been anything that was brought up.

Initial problem: Fuel pump going bad - that's what caused the dying off and stalling, etc.

Second problem: User Error!

Went back out and because I couldn't get the top off the carb, I attacked the float bowl. Took it off - lo and behold, several medium-sized pieces of rubber and other crud.

Diagnosis: When I cleaned the points and re-installed the original fuel pump, I had noticed that the rubber gromits that fit the ends of the tubes were badly decayed. I tried to be careful taking them off and fitting them on. But I must have, in the taking off or the putting on, have shaved some rubber off, or it just fell off into the line and made it's way to the float chamber, where they would have been sucked up into blocking the jet (I'm assuming this) when the fuel flow started to increase.

Sucking up crud? Crud to large to pass the jet? You get no gas!

Take foot off gas? Crud falls to bottom again, just laying there and DARING you to give her gas again. Lol!

I just went TEARING around the neighborhood.

THANKS AGAIN EVERYONE!

Jon

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SOLVED! MGB will not go above 2000 rpm in any gear! #38
mgbgreen Jonathan G California, USA	Posted: March 30, 2012 08:46PM Registered: 1 year ago Posts: 12

Posting this to change the subject line, if I can...

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SOLVED!!! MGB will not go above 2000 rpm in any gear! #39
mgbgreen Jonathan G California, USA	Posted: March 30, 2012 08:47PM Registered: 1 year ago Posts: 12

Just posting to see if I can change the subject line for the thread.

Jon

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Re: MGB will not go above 2000 rpm in any gear! #40
mgbgreen Jonathan G California, USA	Posted: March 30, 2012 08:48PM Registered: 1 year ago Posts: 12

oh well, that didn't work lol

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