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MG MGB GT V8 Factory Originals Technical - Trouble with Holley 390?
today I had some trouble with the V8 and it seems to be related to the 390 Holley on my SD1 Rover V8 engine in the 1973 GT. I did the conversion more than 25 years ago and there were different upgrades and repairs within this time.
General data: 1973 GT, converted 1982-1984. SD1 Engine with 9.35 cr, Offenhauser JWR dual plane manifold, Holley 390 (List 8007) with secondary metering block and Holley choke conversion, 3"K&N pancake air cleaner (engine is deeper in the bay and further back than on most other conversions), dual Mikuni vane type fuel pumps (presure checked at constant 3.9 PSI under load with clean filter in the pipe from tank to pumps), distributer converted to an optical trigger with blackbox (Piranha), copper core ignition wires, LT 77 gearbox, MGC 3.3 rear axle, exhaust manifolds similar to those called the RV8 style.
Today, after a very pleasant ride at temperatures little over freezing point and water temperature in low 80C, I came back into town and the engine died off. It started again on first try every time, but had problems to idle and had very poor response to the excelleration pedal. Oil temperature was about 80C, water temp. read between 80 to 90C in traffic. It became hard to exceed 30 Mph for the last few miles home. The car did not have any backfire at all, so no damage to the power valve has to be concerned, I think.
Back home I checked the ignition timing: 8 at idle, ~28 at 4000 rpm without load.
The inside of the distributer is clean, there is no play in it's shaft bearing and cap & rotor are o.k. All electrical connections on the primary and secndary ignition circuits are o.k., there are no problems with the HT wires and plugs or sparks. The original SD1 coil does not feel hot, just warm. I tried to find air leaks but everything seems to be fine. The mechanical funktion of the carburettor linkages and the lever to the excellerator pump work fine too, the excellerator cam looks o.k. as well.
About a year ago, I took off the carb for an overhault and a general clean up and fitted a new filter (Nissan EFI filter with stainless can).
New gaskets and diaphragms were used and a new power valve too. It worked fine until today.
Before starting troubleshooting in my cold workshop, I am interested in your experiance and advice that might help locating the fault.
BTW, there is no phenolic spacer between the Inlet and the Holley up to now, althoug I can fabricate and add one of 1/4 to 1/2"/max.).
Your thread does'nt say wether you have checked the fuel delivery pressure and flow rate.My v8 died the other day in a similar manner owing to a vane fault on the electrical Holley fuel pump.
Alternatively, I would be looking at the float bowl needle valve or the float itself for the correct fuel level.
both pumps (Mikuni's) are working fine and presure is 3.9 psi. They are connected in parallel, so presure and volume is not a problem.
I checked the setting of the floats by removing the check plugs with the pumps running and both are set o.k. according to the Holley advice.
I forgot to mention in my fist posting, that also the vacuum advance does not have a problem to adjust the timing.
|It almost has to be something simple - like the hose to the pcv valve is broken or came off one end or the other.|
Is the choke opening all the way - is the electric choke wire connected or broken?
Fuel filter to dirty to pass enough gas(oline)?
the fuel filter at the carb was changed about 4K miles ago and there is absolute no dirt or corrosion inside the tank. Even the filter between both pumps and the tank is absolutely clean. I also checked for hoses that came apart but everything is o.k., and there is no PVC valve fitted to my engine, as the tecnical authorities in here did not ask for it.
Meanwhile i took out #1 spark and it looks as if the car is way too much on the lean side.
I will take the carb apart when it becomes a little warmer(we have deep freezer temperatures in here and I do not like to start the heater in the workshop as it will only help to get condensation everywere).
It seems that the quality of fuel has changed and running a hot engine with very cold and dense air semms to be the problem for going that lean, I think by the moment.
--> Does anyone have any experiance with the jetting for the Holey 390 (with secondary metering block) for a SD1 engined 1973 BGT with LT77 gearbox and a 3.3 rear axle runing on 175/80-14 wheels? Due to the position of the engine, a 3" K&N Filter is fitted, so the distance between the air horn and the cover of the cleaner should not be a problem. <--
I am now on 50's for the primaries and on 52's for the secondaries, if I remember it right. What has proofed to be O.K. with this setup?
BTW, the inlet manifold is an Offenhauser JWR dual plane.
Any ideas where to start with sizes?
Your initial post doesn't point to the jets as a problem. Your words, "Today, after a very pleasant ride at temperatures little over freezing point and water temperature in low 80°C, I came back into town and the engine died off..." This tells me everything was fine and then (all of a sudden) something happened (or finished happening).
At this point it seems to be fuel supply - when did you last check the fuel supply and pressure at the carb? Could there be water in the fuel tank?
I checked the presure yesterday after coming back to my workshop/garage. Test utility was a BOSCH engine tester(comparable to the SUN gear). The reading was ~4 PSI. When the engine died off, it was no problem to restart it after bottoming the pedal, so it seems that there is a problem with the primaries of the Holley, as the excellerator pump seems to do enough enritchment for a restart.
|OK, then pressure's good enough (Holleys like 6 psi, but since it ran well before...). But pressure is not necessarily an indicator of sufficient flow (I'm assuming that you are hooking the gauge directly into the fuel line at the carb as a dead head). Try measuring the volume of unrestricted output at the carb into a container. I would expect to see something on the order of 1/2 liter/minute.|
I just can't seem to get away from a fuel supply problem. Could be the needle valve for the float being jammed and restricting flow - just a thought.
the idea with the dual pumps was to create a setup that can deliver sufficient presure, although at the lower end and adequate volume as Mikunis do only 90 liters/h each when floating free.
When I rebuilt the carb some time ago, I forgot to tighten the fuel line with the hose clip at the float chamber and flooded the whole engine compartement within 15 seconds. So the problem seems to be not at fueling the carb but I did not think about the needle valve up to now and will check it this weekend.
Are you real sure there isn't some water in your fuel.
Has your car returned to normal now or is it still running funny. If it is ok now it might have just iced up the carb if it was a cold day. Cheers Willy
My initial reaction was having seen you mention just over freezing temps that the problem was carb icing.
After you leave the car for a while does it tun normally?
Secondary issues are fuel pressure is a bit on the low side, and the timing seems a little retarded for a 3.5 which should be approx 10 deg. at 1000 RPM and all in at 34 deg. by 3500 RPM, were you readings with vacuum disconnected, if so once you solved the main problem I would try advancing the timing, you may be suprised how much this can liven up the engine.
thank you for your information.
I will rejet the Holley to it's stock configuration and switch to a Carter fuel pump. I hope this will help a little.
As fuel quality has become worse within the last few years, the setting I made earlier does not work satisfactonaly any more.
I also will chech the timing after the Carb is set.
When comparing the distributers of the BGT V8, SD1 and Range Rover, I have found a lot of very different timing curves. I still run the SD1 distributer with a Piranhia/Newtronics conversion and the Manual quotes just 22° of total advance for my engine with the original dizzy.
As finding someone for recurving has become very difficult in here and there is no source for springs, I think I will send a spare dizzy to Jeff Schlemmer to do this for me.
Good luck with the re-jet. hope it cures the problem.
Re the dizzy, yes Jeff comes highly recommended, anyone competent in the UK is very expensive.
I took the Holley apart last Saturday and checked everything carefully. Reinstalled the normal 51 and 53 jets and the original shooter. One problem I discovered was a bad secondarys diaphragm that had started to deteorate badly. I also fitted a Mr. Gasked isolating spacer to the inlet and checked for vacuum leaks, but everything seemed to be fine, so took the car for a test drive. Having warmed up with oil temperature at about 80° C, the engine had bad response to the throtle and I checked the ignition again. The pointer is spot on but the strobe cut out at higher rpm, so there is another fault with the distributor or it's electronic, I think. All connections of the LT circuit are o.k. and there are no signs of faults on the HT components.
This evening I changed the HT leads for a set from Excell and will go for an other test tomorrow. Hope I can report about findings then.
|On the road again!|
Seems there were some faults on the V8 but the major problem was obviously the wiring of the fans to the brown wire that serves the ignition switch and therefor the electronic ignition.
When cold, ther was no problem with starting and driving, but when the engine became hot and the fans cut in, there was a drop in voltage and the ignition cut off when exceeding 3000 rpm without load.
I also found a bad secondaries diaphragm on the Holley, beeing responsible for my idea of the engine running on the lean side.
That was well spotted, the current drop on the LT side when the fans cut in, not sure I would have thought of that.
My fans are fed through a relay but the actual power feed may come from the same source.
I did have a similar problem not long ago where when the engine got to 3500RPM it cut dead and the tacho needle went to zero but whilst on the overun the tacho went live again and the engine restarted!
Turned out to be a faulty coil and when replaced with the correct coil, Lucas DLB198 to match the 35DLM8 distributor, no more problems.
This thread was discussed between 17/02/2009 and 03/03/2009
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