1600 Cih Tuning

[Scribe of Lincoln]

Hello All,

Just got my 1600 B back from it's engine rebuild. The bottom end has been completely re-done with crank regrind, new shells, oil pump etc.

The engine pulls well until you reach 50mph and then it hesitates as if it's not fuelling properly. I've been back to the garage and the timing has been checked and is spot on, as is the mixture on the carb. (it has a twin choke Weber with manual choke).

I've cleaned the carb out, the fuel is fresh and has an octane booster in it. The plugs, points, condenser, leads and distributor cap are all new. The only thing I can now think of is that the valve settings may need adjusting?

Anybody got any ideas? I'm now resorting to alcohol.....

Scribe

[stradacab]

Is the fuel pump worn? may not be delivering enough petrol?

[MANTAMAN]

If it only hesitates at higher speed the vacuum addvance to/inside the Dizzy might not be working.

[opel2000]

Don't care what garage says. It has possibly been leaned out to meet emissions.

My bet would still be the carb regardless of Garage, followed by vacuum advance.

Edited September 19, 2010 by opel2000

[lamchop77]

Hello All,

Just got my 1600 B back from it's engine rebuild. The bottom end has been completely re-done with crank regrind, new shells, oil pump etc.

The engine pulls well until you reach 50mph and then it hesitates as if it's not fuelling properly. I've been back to the garage and the timing has been checked and is spot on, as is the mixture on the carb. (it has a twin choke Weber with manual choke).

I've cleaned the carb out, the fuel is fresh and has an octane booster in it. The plugs, points, condenser, leads and distributor cap are all new. The only thing I can now think of is that the valve settings may need adjusting?

Anybody got any ideas? I'm now resorting to alcohol.....

Scribe

Have you had the head/block skimmed. If so the cam timing will be out using the std gears, an adjustable pulley will sort that. Does sound like it could be a fuelling problem though.

HTH

Chris

[Scribe of Lincoln]

Thanks for the replies folks!

I don't think it's the vacuum advance, as when we tuned it up you could see the ignition advancing under the strobe light. Not sure about the fuel pump, but the engine pulls strongly up to 50mph.

You're right about the mixture, which was lean when we looked at it last weekend, however we made it richer and that didn't solve the problem.

During the rebuild, the gauze was removed from the rocker cover - this disintegrated and couldn't be put back in. I'm wondering whether it could be oil "mist" blowing back into the carb at higher revs which is causing the hesitation. I'm going to try another rocker cover (with gauze) next weekend and see if that does any good. I'll be a bit disappointed if it's that, as the original cover is one of the old ones with Opel stamped in the top.

Failing that I'm going to get the GTE dizzy and coil pack put on and chuck the bleedin' points in the bin.....

Any more ideas most welcome.

Scribe

[cam.in.head]

hi there. was the engine ok with regard to this problem before the rebuild or had you not run this engine? i ask because some engine rebuilders re-cut the valve seats down deeper to get rid of any pitting.this can cause two problems .firstly if they are a lot deeper it can reduce the compression ratio, & it will also make the valve springs weaker.this can act as a kind of rev limiter cos the valve can bounch at high revs.does it loose power when the engine reaches similar revs in every gear?.i had a proper gm (gmx) recon engine in mine a while back which had a similar problem.changing the head for a correct one with correct valve heights did improve the problem but not totally. eventually i found that gm had fitted the wrong cam in it !.took me years to find that out!. also remember that a 1.6 does have a different distributor to a gte .fitting a gte bosch one will obviously phisically fit but wont be totally correct in terms of mechanical & vacuum advance curves . how this will affect running will depent on how `standard` or modified/skimmed etc your 1.6 is. just a few ideas to mull over.

regarding valve settings. if its a correct gm standard camshaft fitted then clearances should be 12 thou with engine warm (solid lifters only)

[mantadoc]

Rock the rotor arm around to check for shaft wear. If suspected a blob of LM grease on the points cam and them try it.

Get the dizzy timed up using the maximum advance figure and vacuum advance should be disconnected when setting / checking it.

[Scribe of Lincoln]

hi there. was the engine ok with regard to this problem before the rebuild or had you not run this engine? i ask because some engine rebuilders re-cut the valve seats down deeper to get rid of any pitting.this can cause two problems .firstly if they are a lot deeper it can reduce the compression ratio, & it will also make the valve springs weaker.this can act as a kind of rev limiter cos the valve can bounch at high revs.does it loose power when the engine reaches similar revs in every gear?.i had a proper gm (gmx) recon engine in mine a while back which had a similar problem.changing the head for a correct one with correct valve heights did improve the problem but not totally. eventually i found that gm had fitted the wrong cam in it !.took me years to find that out!. also remember that a 1.6 does have a different distributor to a gte .fitting a gte bosch one will obviously phisically fit but wont be totally correct in terms of mechanical & vacuum advance curves . how this will affect running will depent on how `standard` or modified/skimmed etc your 1.6 is. just a few ideas to mull over.

regarding valve settings. if its a correct gm standard camshaft fitted then clearances should be 12 thou with engine warm (solid lifters only)

Thanks for the reply. Before the engine was rebuilt I didn't dare do more than 50mph, as the bottom end was completely knackered, so difficult to say whether the problem was there before (the car had been off the road for 4 years when I bought it). The head was not touched during the rebuild, as it was found to be OK, however the garage "set the valve clearances" when they refitted the engine. If they got these wrong could that be the cause of the problem?

Rock the rotor arm around to check for shaft wear. If suspected a blob of LM grease on the points cam and them try it.

Get the dizzy timed up using the maximum advance figure and vacuum advance should be disconnected when setting / checking it.

Thanks for this. They didn't disconnect the vacuum advance when setting the timing - should they have done that?

[MANTAMAN]

a Dizzy has both mecnanical addvance (usually 'bob' wieghts in the dizzy) and vacuum addvance (a pipe from the inlet manifold). The vacuum addvance should be disconnected when timming the ignition but addvance will been seen with a strobe light from the mechanical addvance.

You can test the vacuum addvance by sucking on the manifold end of the pipe while watching a strobe timing light.

[opel2000]

I always used to remove the gauze from the rocker covers anyway, as they were generally so gummed up that any crankase fumes were not actually breathing through as they should have done.

Never had any probs with this ever, and that has been on a lot of Manta's and they were pushing out good horses on the rollers too.

I have had problems with flat spots and hesitance on carbed Manta's before, on one occaision after constantly checking everything over and over again it was took to a rolling road where they eventually found it was the mixture, basically the jets on the carb were not suitable for the flow through the head, they simply drilled out (as they had no replacement jets) for the carb and all was fine.

Have said this time and time again in the past............

Garages can only set up a baseline mixture for emissions tests, THE VEHICLE UNDER LOAD NEEDS IT'S CARB TO BE SET UP ON A ROLLING ROAD.

[plumster]

You have a very similar lump to mine, at one time she was a real lazy bitch, I contacted a local roller tune up place, got them to fit a weber maintenance kit to the carb & do a rolling set up, sweet as a nut since then.

Good luck.

[lamchop77]

I always used to remove the gauze from the rocker covers anyway, as they were generally so gummed up that any crankase fumes were not actually breathing through as they should have done.

Never had any probs with this ever, and that has been on a lot of Manta's and they were pushing out good horses on the rollers too.

I have had problems with flat spots and hesitance on carbed Manta's before, on one occaision after constantly checking everything over and over again it was took to a rolling road where they eventually found it was the mixture, basically the jets on the carb were not suitable for the flow through the head, they simply drilled out (as they had no replacement jets) for the carb and all was fine.

Have said this time and time again in the past............

Garages can only set up a baseline mixture for emissions tests, THE VEHICLE UNDER LOAD NEEDS IT'S CARB TO BE SET UP ON A ROLLING ROAD.

Totally agree, the only way to set up properly is on a rolling road. The 2.0 race motor i first ranwas set up using the gunson bits and bobs and according to them was right, but the car just didn't seem right, bogged off the line and seemed to run out of go at the top end. One rolling road session later minus 80 quid and 20 bhp had been wrung out of the motor, was a totally different engine after that.

Book in to a reputable one and go down with spares dizzy, coil, bit n bobs as they may find problems with them.

Cheers

Chris

[Scribe of Lincoln]

Thanks again to all who have replied. The car is now back in the garage having the carb stripped down and cleaned out and the timing checked again. Hopefully I'll get this sorted before the end of the month when it runs out of tax and goes away for the winter!!

I may go down the rolling road route in the new year - does anybody know of a reputable one in Lincoln / Horncastle / Louth area?

On the plus side I managed to get the boot light working at the weekend...........

[Scribe of Lincoln]

A postscript to my tuning saga.

The car went back to the garage, where the carb was stripped down and the second choke was found to be seized. This was unseized and put back together and with a new choke cable I thought Bob's your Auntie. The car ran OK when I drove it home on Friday so I thought I'd be brave and go and blow the tyres up. After six miles I spluttered to a halt tonight on a dark country road. 1hr 20 mins for the AA to turn up with only a MW radio for company - the music was OK but my French is not that good....

Turns out all that's wrong in the earth for the condenser. The barrel of the condenser was moving around inside the c-shaped clamp it sits in inside the Delco distributor (no wonder they changed to Bosch after a couple of years!). A new condenser and it's running fine.

Electronic ignition next year methinks!!!!

[opel2000]

Good to know it's all sorted mate.