Moss Motors, Ltd

Recently I exchanged the engine in my 77 MGB due to low compression and oil blow by.  I used a motor from an earlier model and had to change the front engine plate to get the late model motor mounts to work.  Now that the motor is installed I have great steady idle but very low acceleration and poor power, at 2000 or so RPM under load the power boggs down and I barley have any acceleration at all.  I suspect I set the timing chain off the mark by a timing tooth or two.  Is there a way to tell I made this mistake without pulling the timing chain cover?  Will checking with a timing light reveal more about the issue?  Idle is great, steady and strong, other than the timing chain the valve lifters were inspected and valves have been double checked for clearance, a new clutch and presure plate was installed at the same time.

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Randy Raley
Knoxville, TN
rraley@nxs.net

I like to use a vacuum gauge to set the timing on old engines where things like a stretched timing chain, worn sprockets, dizzy drive gears, etc. have altered the accuracy of the timing marks on the damper.

You'll need a vacuum source from the intake manifold, such as one that operates the brake servo.

 Here's a guide and another link that you might find helpful.

http://automotivemileposts.com/garage/v2n8.html

AND

http://www.secondchancegarage.com/public/186.cfm

I checked the timing using  a strobe and set it to 14 degrees per the engine number and the manual.  I checked the compression #1 cylinder had 135 lbs and 122, 142 and 132 respectfully.  Valves are set and double checked at .013.  Throttle body opens fully when accelerator petal is pressed and the distributor and carburetor were used from the old motor that had plenty of power considering the compression was way off and it had serious oil blow by.

 Power is still very low with a low throaty sound and rpm not reaching much over 3000 under a load, it will rev a bet higher on an open road under light load but the low throaty sound is significant over 2800 rpms or so.

Thanks for the links to vacuum setting the timing I will look into that a bit more I had no idea vacuum could help set the timing, do you think it might still be an issue?

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Randy Raley
Knoxville, TN
rraley@nxs.net

Hi

  being a 77 MGB I am asuming it has a stromberg carb. The symptoms you describe sound like a hole in the carb diaphram. The throaty sound is the suck through the open butterfly as the engine tries to suck in gas and air, but if the needle is not lifting then not enough fuel is coming from the jet. Strombergs can also block in the jet, restricting fuel as well. To check your timing mark, bring the no 1 piston to to top dead center, check it is at the top of it's travel by looking down the spark plug hole as you rotate the engine. Confirm that both valves on no 1 cyl are closed. The timing mark should be on the 0 deg marker. It is easier to have some one else to look at the piston as you rotate the engine to spot the top of its travel. Another thing could be a tired fuel pump = not enough go juice. Or a major air leak in the manifold.

Hope this helps

   Mark

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1958 MGA coupe ( under restoration
1972 MGB GT
1995 Ford Bronco
2004 Pontiac GTO

Well I have replaced the original Zenith Carb with a downdraft Webber.  It appears to be working okay, linkage and outside appearance is good.  When the engine was replaced I only removed the intake manifold with the carb attached and replace it at the manifold only, the carb was never off the manifold.  It was used on the old motor and seemed fine there.  I have checked the performance of the carb with the air filer off and with the motor running about 2500 rpm, holding the throttle linkage open to attain that rpm and dumping a capful of fuel directly down the butterfly opening.  When I did  that nothing happened no increase in rpm no extra throaty sounded it like it did not even know the fuel was there.

I did flip the carb upside down while it was off the old engine could a float or other internal part be stuck internally any ideas would be helpful. 

 

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Randy Raley
Knoxville, TN
rraley@nxs.net

GOT IT!

 When I did the exchange on the engine one of the header washers that holds the intake and exhaust manifolds to the head got caught inside the header exhaust unnoticed.  When I started the car initially it the pressure blew it threw the header and it fits perfectly into the opening in the muffler. The 1.25" washer fits perfectly into the 1.5" opening in the muffler reducing the exhaust flow to less than .5".

 I replaced the muffler and it runs like a top.

 

I actually heard a suspicious sound when I started the engine the first time, now I know what it was.

Drove it out TN hwy 129, the tail of the dragon, last week and had a blast, shes a head turner for sure and pleasure to drive.

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Randy Raley
Knoxville, TN
rraley@nxs.net

Congratulations! There's no greater satisfaction then solving those mysteries by finding the little gremlins - like a washer...