High Idle And Pulley ?

[thailoz]

Ok I have a worked 4k

 

280 duration Cam

 

std 4k Carb

 

2 inch exhaust

 

Electronic Dizzy

 

I am running it on a test bed starts well but I can not get the idle down below 11- 1200 rpm

 

I have checked and replaced all the vacuum hoses I have only three connected as follows

 

advance pipe from Dizzy to heat shield spacer at the bottom of the carb

 

pcv valve to the same plate

 

choke thingiy from manifold

 

See Pictures below

 

The carb was rebuilt and double checked for settings it runs well and revs cleanly

 

 

 

 

Question 1 does there need to be gaskets either side of the heat plate ?

 

Problem 2 I have taken number 1 plug out and turned the engine over so piston is at TDC rotor pointing at number 1 plug lead on cap (central to number 2 plug as stated in 4k engine manual) both valves free i.e. closed But the timing mark on the pulley is way of see below pic .I have checked the pulley for other timing marks and there is just the one.

 

Is it possible the cam timing is way off ? when I put the cam in the head was off and I put the piston to TDC lined up all the marks as per book.

 

thanks in advance

 

Laurence

[Banjo]

Hi Laurence,

That's some project you've got going there !

 

Re timing mark for TDC. Your last picture does not show the timing mark. Not sure what the little red mark is pointing to. The TDC No: 1 timing mark is a small indent in the rear of the crankshaft pulley, nearest to the advance/retard timing markings, on the timing chain cover.

 

In your picture, the fan belt obscures this area.

 

There is an indent on the front of the outer pulley, in the approximate right area of rotation, but that is unusual, from my experience.

 

If the timing was way out, I would not think you should be getting the "clean" reving results you are.

 

I'd suspect it is sucking air somewhere, or the distributor is not timed correctly.

 

Unclamp the distributor slightly, and while it is idling at 1100 - 1200 rpm, rotate the dizzy slowly clockwise, and see if it has an effect on the idle rpm. Also pull the rubber hose off the dizzy vaccum advance, squash the end of the hose together, and see if that makes any difference to idle.

 

The results of these tests might point you in the right direction.

 

Cheers Banjo

[thailoz]

Thanks for the quick reply banjo

The red mark is where a line is across the front pulley

I've just taken the belt off and scraped the paint off the rear pulley and I can just make out a tiny indent .

I've smeared some liquid paper over the area and wiped it off sure enough a very small line was left as luck has it it lines up with the 10 btdc mark ( I read somewhere that's what a hot cam should be set too).

 

I did try moving the dizzy and turned anti clockwise it speeded up and clockwise slowed her down then I ran out of movement. At first I had the Vacuum pipe connected direct to the manifold and it raced took it off and she slowed now its connected to the carb plate it is better. need to get some more fuel and try again Would plugs make a difference I can't get the BE529Y plugs but put a plug with a long reach electrode same 5 rating (twin squish head)

 

Laurence

Edited April 8, 2015 by thailoz

[GJM85]

You should use a gasket on both sides of the heat plate(insulator).

 

You shouldn't need any vacuum hoses connected to the dizzy with that camshaft. Although the engine appears to idle smoother with manifold vacuum to the distributor, it's actually just idling faster and makes it difficult regulate idle speed. With 10 degrees base timing and the manifold vacuum on the distributor it will have about 20 degrees advance at idle.

 

10 degrees advance is good base timing. Idle would be ideal around 1000rpm. No higher.

 

Possible vacuum leaks aside, I believe your biggest problem will be fuel starvation at idle. A cam with 280 advertised duration will have considerable overlap, poor compression, low vacuum and an uneven idle so keeping the keeping a rich idle mixture will help a lot.

Edited April 8, 2015 by GJM85

[LittleRedSpirit]

Yes and in general any cam that presents as lumpy at idle will want to idle a little higher than a stock cam that provides plenty of vacuum and a smooth idle character.