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"B"ad performance

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Bob Claffie

Bob Claffie

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"B"ad performance

I'm a new guy and want some opinions. I rebuilt two MGB engines recently (mine and my sons) to stock factory specs. His is a '71 and is a real zippy performer and mine is a '72 and is a god-awful dog. Can ALL the performance difference be attributed to the carbs differences? His has HS4's and mine has HIF's? If the carbs are more or less equal what could I have done wrong to make them run so differently. Both get similar fuel mileage, use no oil etc, start quickly. I'm stumped. Thanks, Bob
 
Re: "B"ad performance

Hi Bob, and welcome to the forum. I really don't think that the difference can all be down to the carbs, but there may be differing opinions on this. You will get plenty of input .
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Re: "B"ad performance

My suggestion send your son off to camp and switch engines
 
Re: "B"ad performance

I have a set of rebuilt HS4's sitting on my workbench just waiting for good weather, then maybe I can prove one way or the other if that is the key factor in my B's lack of acceleration. Cruising is ok although it doesn't go up hills with much vigor. Would missing one tooth on the timing set-up account for it's lack of low speed performance? Grabbing at straws now. Bob
 
Re: "B"ad performance

Hey!

I kinda like my engine in my car. I think I'd notice the difference if they got switcheroo'd on me.

Bob's kid
 
Re: "B"ad performance

First thing...change the password on your computer so Junior can't snoop on you.
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OK,

Set plugs and timing the same, run for a while and then...

1. I'd look at plugs to see if both cars are about even, mixture-wise.
2. See if timing advance is about the same (check from idle up to about 4000 RPM...see if spark "moves ahead" on pully about the same amount)
3. Compression test both cars and compare
 
Re: "B"ad performance

I gave the kid 5 stars for the answers in his profile, we need more young people in the Brit car hobby to see that the future is continued
 
Re: "B"ad performance

A lot of times distributers have been switched over the years. Just because they look the same, doesn't mean that they are!! If you have a distributer that is not allowing enough advance, it would be quite doggy!! If your vaccum advance is plugged into the wrong place on the carburator it would not work right either!! I think that if you missed a tooth, it would be very obvious!! Also, by the sounds of things, you have enough expeience that you would have double checked it!! The other thing to check (if you didn't replace it) is your cam!! You can check for a worn lobe with a dial indicator! Barring all that, send the kid to his room and take his engine!!
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Re: "B"ad performance

I checked out the young man's website Gary. I think he's a bit old for that
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Re: "B"ad performance

https://www.bnsracing.com
is my hobby site, as an alleged motorsports journalist

https://www.claff.net/claff/cars
shows all the cars I've had, including the dreaded MGB. The two most recent cars, both blah four-door sedans, aren't yet up there.

FWIW concerning dear old dad's car, it might be a snoozer on the road but long-term wise, it's a much better prospect (i.e. it is steel in places my car hasn't been steel in quite some time).
 
Re: "B"ad performance

Chuck: Already did that. My (dad's) car is a composite of a good solid shell from a '71 with the innards of a low miles, clapped out, totally rusty '72. Ended up with just about the right mix of "good" parts to make one decent looking, almost decent running b. Even got two ok tops, one of which was donated to son's b. Down side, between both cars and left over spares we don't have a legal set of tires between us! Bob
 
Re: "B"ad performance

Gary: Click on the second of the two web sites listed. The MG is the second one down in the right hand column. Bob
 
Re: "B"ad performance

Just thunbing through my Victoria British cat and noticed that the cams for 71 and before are different from 72 and newer. Perhaps this could have something to do with my lack of performance. I have a spare motor but the previous owner copped the id plate off it to put on a bogus motor for his car. All I know is that it is a 5 bearing engine. The question is: are there any distinguishing markings on a cam that I could possibly use for determining the year? Thanks, Bob
 
Re: "B"ad performance

As the owner of a '74 ungoing an engine rebuild, I'd put my money on the cam. The '72 has the 18V series engine, where the cam timing was retarded by 4 degrees to improve idle emmisions, and off the line torque (see 'Power Tune your MGB' book by Peter Burgess). Conversely, this takes away from the top end. I am replacing mine with a Piper 270, after getting soliciting opinions from various places, including this forum. Also, the distributor advance curve will definately have an effect... get out the timing light!

Good luck!
Dave
 
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