brand new re-build- jetting a weber with a new cam

[Anonymous]

Well, I finally got my big re-build ready to go. I can't wait to post pics- it looked really good at first anyway. I painted the motor chrysler gold, polished the offy 3x1 set up and and cleaned and re-painted everything. I guess I bit off more than I could chew here because I did everything at once and now I have no baseline.

The carbs are new, the cam is new, the 3-row radiator is new, the thermostat and water pump are new, and the distributer is new.

I started out with with a 3 weber set up, and a Unilite mechanical advance distributer but since I couldn't tune them for anything I ended up blocking the outer carbs and installing my old Duraspark just to start simple and at least get it to run o.k. for the break-in period. So now I just have basically the same motor as before with a single weber 34ich and a new clifford 260h cam and bigger valves but I can't get the motor to idle reliably below about 1000 rpm and it seems to run a little hot at around 220 degrees.

My last set up was a weber 38dgas and I always tuned it by dropping the idle to around 500 and backing out the mixture screw until it was right.

This one I cant seem to get to idle that low so I have no idea where to set the mixture screw.

I know the cam is supposed to be a little rougher idle than the stock cam but I can't even sit at traffic lights without my foot on the brake if it has to be this high.

Any ideas what the problem may be? I put the biggest idle jet I have in there, which is a size 60, but it is hard to know what it should be if I can't set the idle down into tuning range. I set the timing same as always. And I checked for vacum leaks by spraying some starting fluid around and it all seemed good (though that offy adaptor could leak from the bottom and it would be hard to find). I always heard that leaks caused an up and down idle and this is just plain rough below 1500rpm or so.

Help guys- I couldn't have gotten this far without you all and now I need a little more educatin' to pull this thing off I guess.

 

[Junk-Falcon]

ppp

 

[Anonymous]

yes, I got the jet holders from Todd Fields. I left off the selenoids, even on the center carb figuring i would put it on if I ever have run on problems.

If 60 seems good for the idle jet, what else would cause the rough idle? or is it "normal" with the 260 cam?

 

[Junk-Falcon]

ppp

 

[Anonymous]

thanks for the replies Junk. yes I got adjustable rockers off an old 140 and rebuilt the whole assembly. I adjusted them twice so the pushrods just barely couldn't be rotated when closed but I'll definitely double check.

That question about the cam chain just plain scares me. I sure wouldn't want to tear it down that far again. Anyway, wouldn't that make it run bad all through the rpm range? Mine sings when I give it any gas at all.

If anybody has a better way to check for leaks than spraying starter fluid I'd love to hear them. I don't think the starter fluid trick works on the underside of an offy adapter. Maybe I'll just pull it apart and add another gasket under the center carb just to eliminate that possibility.

 

[Anonymous]

"I set the timing same as always."


How was that? Are you using a different balancer than what came off? A vacuum gauge is sometimes invaluable when you know the idle mixture/speed and timing are in question. You'll want to try and find a nice vacuum reading. I'm curious to see what it's pulling. Should be up around 15", maybe a little higher, depending on some variables.

 

[Anonymous]

Normal for me is 10BTDC and I checked the tdc mark before I put the head on it. Today I re-checked the valve adjustment and took apart and re-nstalled the offy adapter with another center gasket. It is a little to late to fire it up now , so we'll see in the morning if that fixed anything.

I have never used a vacum guage before- maybe it is time to learn.

 

[Anonymous]

Junk Falcon is the winner! After re-installing the adapter to make sure there are no vacum leaks and about two days of testing and re-testing everything I got it to start but it seemed to be running on 4-6 cylinders and had no power. So I figured I would re-adjust my rockers for the fourth time. This time I tightened them until I couldn't twist the pushrod then LOOSENED them 1/8th turn. The performance handbook recomends tightening 1/8th turn but than seemed too tight for my motor. Anyway now it runs and idles right.

I never had an adjustable rocker motor before so I didn't know the symtoms when it is out of adjustment. It acts just like the timing was off or something. Anyway, I learned something this week.

How can you tell if the valves are too loose- noise?

 

[Junk-Falcon]

ppp

 

[Anonymous]

I think valvle lash adjustment is becoming a lost art - except for us biker types, that is...

A ballpark number for these valves, because of their long stem length, would be to have .002" clearance on the intakes and .006" on the exhausts. This happens to be the same numbers used on the solid-lifter 390 engines of the mid-1960s that I had.

Turn the engine until the piston is TDC on the compression stroke for the cylinder you're adjusting. Then slip a feeler gauge in between the rocker and the top of the valve (.002" intake, .006" exhaust). Tighten the adjuster gently until there is light drag on the feeler gauge. Tighten the adjuster's lock nut and re-check, using a feeler gauge that's .002" thicker than your desired limit (that's .004" for intakes and .008" for exhausts). This thicker gauge should not be able to get in there, but your standard size should be able to slip in & out of the valve-rocker contact spot.

I hope this is clear.

The mechanics of the valve train that is causing your problem is: warm valves grow in length. The hotter they get, the longer they get. If you set them to 0.000" cold, they will never close when warm. If you set them to cold clearnces equal to hot-growth length, then they will close, even when warm. If you set too much clearance, they get noisy. Here's one caveat, though: if you plan on lots of high-revving action, add .001" to the clearance. This is needed because oil on the cam face has a difficult time of "getting out of the way" at high RPM and can end up causing the pushrods to "float" and extra .001" higher at speeds above 4500 RPM. If you use thick oil, like 20w50, add ANOTHER .001" for hi-RPM for the same reason.

 

[Junk-Falcon]

ppp

 

[Junk-Falcon]

ok i was rereading the way you adjust the rockers, one point i need to make

 

[Anonymous]

Junk- your description sure sounds right. The last motor I worked on you were even supposed to leave a little clearance checked with plastigauge.

But the The Schjeldahl's falcon six performance handbook says "tighten until you can no longer rotate the pushrod. Tighten an additional 1/8 to 1/4 turn" this didn't work for me. so I loosened them 1/8 turn. But now I am worried that it still may be too tight. I don't want to wear out my cam or anything.

Maybe we can get a comment from David or Dennis on this one?