Engine Limited to 4000 rpm?
Posted By : David Rumens, 03-Apr-2005, 02:41pm
I take it the lack of revs are in any gear and the problem was there before you changed over to the present ancillaries. The first thought is the Rev
Counter working correctly and what type is it. Is it the 1500 electronic type or have you retain the 1300 Dizzy and therefore have the mechanical type
which are some what inaccurate. Also if you have retained the 1300 Dizzy it may not have help matters though I do not beleive either this or the Rev
Counter are the real cause of the problem.
Secondly thought was it may be a lack of fuel in the float chambers. This could be caused by a faulty fuel pump, or a block in the fuel pipes.
Secondly thought was it may be a lack of fuel in the float chambers. This could be caused by a faulty fuel pump, or a block in the fuel pipes.
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Engine Limited to 4000 rpm?
Posted By : Roger Cuthbert, 03-Apr-2005, 06:17pm
The lack of revs are in all gears.
Too be honest I don't know if the problem was there before changing the ancillaries - The inlet manifold and carbs were changed almost as soon as I got the car so it wasn't driven much in this 'original' condition.
It's interesting that you mention the dizzy - I've thinking about this this afternoon in fact!
It has the 1300 AC Delco dizzy with the mechanical drive to the rev-counter. I'm wonderng whether having the 1300 dizzy is the cause or not.
I was considering switching the dizzy to the 1500 Lucas model but I'm a little unsure where this leaves me with regards the rev counter - not sure that I would be able to swap out the rev counter for an electronic one as the wiring (and ???) probably aren't there?
I don't believe this to be a fuel issue - the fuel pump was replaced last year and is delivering fuel (at least to the carbs...).-
Engine Limited to 4000 rpm?
Posted By : David Rumens, 03-Apr-2005, 07:21pm
You would need to add an extra couple of wires to fit the 1500 Rev Counter. The spade connector on the counter goes to the ignition switched supply and the bullet connector on the counter goes to the points. The case of the counter must be earthed.
A 1300 Dizzy would not help the situation, but it should still rev above 4000 rpm with this fitted. Before changing it I would first check the 1300 Dizzy mechanical advance is working. See if you can move the rotor arm by hand and it springs back to its orginal position when you let go. If you cannot move the rotor arm then the advance weights may be stuck and require freeing off.
But bearing in mind the problem may be on the present ancillaries one other cause could be sticking pistons in the carbs. Carefully take out the pistons and clean the piston and dashpot cover.
Also if the needles and springs have not been changed to match your air filters and exhaust system this would restrict the rev range. With the set-up you have the needles should be AAT with yellow springs.
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Engine Limited to 4000 rpm?
Posted By : Roger Cuthbert, 03-Apr-2005, 07:50pm
David
Appreciate your comments - at least I know can fit an electronic rev counter if needs be!!
I'll check the advance mechanism on the dizzy as you suggest - always worth checking the obvious first!
I don't think sticking pistons is likely to be my problem - the carbs were completely stripped down last summer when they were fitted. Again, obviously I'll check this to be sure...
A valid point that I hadn't considered was the needles and springs. I don't know what needles are fitted. Seems I have a few things to be getting on with next weekend.
Again, appreciate your help and will advise as too where things progress.
Roger-
Engine Limited to 4000 rpm?
Posted By : Tim Willis, 03-Apr-2005, 11:08pm
I think we are all thinking too complex here. What about checking for wide open throttle, the cheapest and easiest source of power for our cars. I get them in all the time with only 30 to 50% throttle opening. If the engine is performing well as you say there is no reason to suspect it. Check the cable adjustment, check the crank in the linkage is returning to stop on the manifold casting, and check the adjustable stop on the throttle pedal isn't restricting.
Tim
Willow Triumph-
Engine Limited to 4000 rpm?
Posted By : Duncan Banks, 03-Apr-2005, 11:19pm
When I built a 1500 with twin box system, free flow, filters mk3 cam and ported 218141 head I had the same problem. Just no go when revs got up with the loud pedal on.
The fix was as Nigel suggested, the wrong needles and springs. Without a rolling road I ended up with AAA's and yellow springs.
Hope this helps
Duncan
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Engine Limited to 4000 rpm?
Posted By : Roger Cuthbert, 04-Apr-2005, 07:46am
Duncan
A little more advanced then my setup but always good to hear a solution to a similar problem...!!
I'm going to try this solution as it's not going to break the bank to get new needles and springs.
Weather permitting I'll do this next weekend and post results. I'm also going to clean the dizzy out just to be sure the advance mechanism is functioning correctly.
Roger-
Engine Limited to 4000 rpm?
Posted By : Colin Wake, 04-Apr-2005, 03:15pm
You will need 2 stages richer probably if no-one else has mentioned it.
In the meantime, you could try pulling the choke out a bit when it starts to get breathless. If it feels like a second coming then richer needles are the way to go.
Colin -
Engine Limited to 4000 rpm?
Posted By : David Rumens, 04-Apr-2005, 06:24pm
AAT needles and yellow springs are normally recommended for your set-up.
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Engine Limited to 4000 rpm?
Posted By : Roger Cuthbert, 05-Apr-2005, 07:34am
I've ordered replacement needles and springs for the carbs.
I went for AAQ needles - advice was AAT for K&N filters and sports exhaust setup on a lean mixture - AAQ for same setup (but 'not lean' - normal...?)
Fill fit at the weekend when I will also check the dizzy advance mechanism.
Will post outcome...
Roger-
Engine Limited to 4000 rpm?
Posted By : David Rumens, 05-Apr-2005, 05:59pm
Sounds right. AAT gives good performance and MPG. AAQ will give a tad better performance an AAT but at the cost of the MPG.
Its personal choice.
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Engine Limited to 4000 rpm?
Posted By : Roger Cuthbert, 16-Apr-2005, 05:34pm
Bit of a delay actually getting the new needles and springs but have them now and have fitted them.
They have made a noticable difference - still doesn't seem quite right but it's much improved on what I had.
Spent today 'tweaking' a few other bits - carb balance and mixture following the new needles/springs, dizzy/points/plugs etc... All the basics.
Still need to recheck the timing - sun was too bright...! I also want to verify the accuracy of the rev counter.
Still a few things to be playing with. Appreciate the assistance offered by all, especially David.
Roger-
Engine Limited to 4000 rpm?
Posted By : David Rumens, 16-Apr-2005, 05:40pm
Roger, Any thanks for the feedback. Hope your engine BHP goes up to around 80.
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Engine Limited to 4000 rpm?
Posted By : Roger Cuthbert, 04-Apr-2005, 07:42am
Tim
Good call but already considered this one...!!
This isn't the issue either - pedal up and the throttle is fully closed on the carbs. Press to the floor and the full travel is there, i.e. no 'spare' travel at the linkage.
Suggestion appreciated anyway.
Thanks
Roger
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Engine Limited to 4000 rpm?
Posted By : Nigel Gibbins, 03-Apr-2005, 05:50pm
Roger,
You say that the engine runs out of revs at 4000 rpm, but you don't mention any misfire, vibrations, fuel starvation or infact any other symptoms except that the power just dissapears.
If this is truly the case the I would suspect your timing advance mechanism isn't working properly, the only way your can check this is to use a timing gun and run the engine up.
Co-indentally the dizzie's we use on spittfires reach maximum advance at 4000 rpm (or should) and maybe yours is simply never getting there (max advance that is)? It could be caked with filth and just in need of a good clean around the advance weights.
You say that the engine runs out of revs at 4000 rpm, but you don't mention any misfire, vibrations, fuel starvation or infact any other symptoms except that the power just dissapears.
If this is truly the case the I would suspect your timing advance mechanism isn't working properly, the only way your can check this is to use a timing gun and run the engine up.
Co-indentally the dizzie's we use on spittfires reach maximum advance at 4000 rpm (or should) and maybe yours is simply never getting there (max advance that is)? It could be caked with filth and just in need of a good clean around the advance weights.
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Engine Limited to 4000 rpm?
Posted By : Roger Cuthbert, 03-Apr-2005, 06:25pm
Nigel
There are no other symptons - it simply seems to run out of power. Change up a gear and all is fine (unless I'm already in 4th...!)
Another post also raised dizzy issues. I have the 1300 AC Delco dizzy fitted with the mechanical drive to the rev counter. I'm wondering whether I need the 1500 Lucas dizzy but this raises the issue of the electronic rev counter - not sure if this can be fitted into a Mk IV (thinking connectors, wiring, etc)?
Certainly it's worth a good clean of the advance mechanism before charging out with the credit cards again...
As I recall, the advance was doing something - when I did the timing last I checked the advance was happening when the revs were increased - not sure how much advance I should get in total when up to say 4000 rpm - any idea?-
Engine Limited to 4000 rpm?
Posted By : Nigel Gibbins, 03-Apr-2005, 08:58pm
To be honest the type of dizzy is not the issue. Our cars will run on either Delco or Lucas... I've run 1300 and 1500s on both without any problems whatsoever... after all, all it does is tell the coil when to procude a spark
I've read about needle suggestions and carb pistons, but I don't think that'll be the problem either. If the pistons were sticking they would most likely be sticking in the 'full acceleration' postion (ie up) and that you richen your mixture. If your too rich due to needles then you would have other symptoms like a 'lumpy' power delivery at high revs and black smoke from the exhaust.
If the pistons are stuck down then you'd be too lean and accelleration would be seriously hampered. If it were too lean (even due to needles), then the engine would begin to 'pink' at high revs (sounds like a diesel) and the power again would be 'lumpy' (i.e. like a misfire).
I acutally think you're probably on the wrong needles anyway (about 95% of our cars are) but, like everyone else, you are within the usual '80% right' margin (i.e. 80% of the ay to being the right needle) and that's perfectly good enough for road use. You'd need rolling road help to narrow the needle down to by that last 20% margin for error. But the difference... wow! That's partly how Class A racecars can get 112Bhp AT THE WHEELS on SUs!!-
Engine Limited to 4000 rpm?
Posted By : David Rumens, 04-Apr-2005, 06:14pm
The main difference between the 1300 and 1500 Dizzy will be the advance curve which could effect the performance.
Sticking carb pistons do limited the rev range as there will limit both the fuel and air available to the engine. All that happens is the piston will not rise to its full extent, when the throttle is close the springs will force the pistons back down. Not an uncommon problem with SU carbs
As for wrong needles and springs. If these are the standard on the present set-up the mixture will be too weak and this will have the effect of limiting the top end. In theory it should pink but pinking is very difficult to hear at high RPM. I agree the overall performance would also reduced.
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