Not low end ~ Help!

[lrdg]

I’ve been lurking around here for a couple years and seem to ask a question about once a year. So, here’s 2010’s question. The truck is a 1984 Bronco II, engine is stock 2.8 with less than 100,000 miles since rebuild. Ignition is duraspark, the distributor was purchased new (rebuilt?) from NAPA, and the control box was out of a yard. The Carb is a 2150 / 1.08 off a 1978 Mustang II. When I did the conversion I was very happy with the possible exception that it seemed like it should have had a bit more top end. For that last few months I have lost the bottom end. It will only crawl away from a stop, such as a stop light. It will just barely go up a hill . On the flat it will run along 60-65, no problem. It feels for all the world like a timing problem. I have adjusted timing repeatedly. I have set it between 8 deg. and 15 deg. BTDC with the light, I’ve tried setting it by vacuum, I’ve tried adjusting it by ear. I cannot get it. A couple days ago I found the vacuum modulator on the tranny was sucking ATF so I changed that out. Just for grins I stuck a 2150 / 1.21 on to see if it made any difference. It didn’t, but I did find that I don’t really want to do that in the Arizona desert ion the early afternoon. I am a shade tree sort of guy and have built engines so I’m not completely ignorant but as its all sort of hobby there seems like always something I’ve missed. Any suggestions or similar experiences?

Thanks!

 

[Big Jim M]

If it doesn't chug & miss then it is running Ok. The problem you describe can be stopped up (partly) exhaust system.. Or the air cleaner... But It could also be the vac advance not advancing and the timing isn't where it should be.
Make sure the timing is at 36/40* at 2800 or so.
There is always a small possibility the carb isn't opening all the way.
Big JIm

 

[kimcrwbr1]

+1 on the exhaust something you have done should have changed it. I am running a 2150 with 46 jets and still have plenty of lower end and can pull a pass at 60 mph with a three speed auto. Did you try putting your hand on the tail pipe and have someone goose it if there is little change on the air coming out you have a restriction either cat or muffler I am still running a cat with a new muffler. if your compression is still good and have good oil pressure check the vacuum pressure you should have 17-20 hg with the vacuum advance on manifold pressure at an idle and around 20 above 2500 rpm. If you havent block the egr using the gasket that comes with it and a 1/4 plate the vacuum guage will also tell you the overall health of the engine with a fluzuation of not over 1/2 hg at a idle. GL keep us posted

 

[lrdg]

Well, a couple other things I tried...

Disconnected the exhaust at the front (intake) of the cat converter. Sounded interesting but no real change.

Checked the vacuum advance by taking the hose off the carb and going to intake vacuum. The spark did advance.

I put a vacuum gauge in the carb and the vacuum does rise with rpm.

I have a vacuum gauge on the intake and tend to run 15 to 18 lbs at idle.

This afternoon I went back out in the sun and changed out the control module. No report as the battery is charging. I will get back out in an hour or so (when the sun is down some) and try it out.

Thanks for the thoughts. I'm sure its something I just overlooking. It really helps to have several ideas to look at. Thanks Guys! http://www.therangerstation.com/forums/images/smilies/icon_cheers.gif

 

[Hotrodlincoln]

If this has developed over a period of time it could be worn timing gears.
If it just started one day out of the blue maybe the EGR valve is stuck partially open.

 

[lrdg]

Boy, I hope it's not worn timing gears, the engine is less than 10,000 miles old.

No EGR any more. No air pump.

 

[martin]

Did you check if the mechanical advance is working, it does sound like a timing issue.

 

[kimcrwbr1]

It should be advanced to around 37 dbtdc at 2500-3000 rpm I found mine runs better with manifold vacuum for the advance. Did you take a vacuum hose and go around to all the gaskets and fitting and listen for vacuum leaks and does the vacuum guage hold steady at an idle. It could be leaking betweeen the ports where the egr is blocked off get a new gasket for a couple of bucks and just replace it with a good metalic one. I had a problem with mine leaking around the base of the carb. I took the carb off and glued a piece of 100 grit sandpaper to a piece of flat plywood and sanded the base of the carb flat careful not to gouge it and there is a carb spacer for a 302 felpro #60529 for $18 that adapts the 2150 non feedback carb perfect my vac holds steady at 18 hg now. the vacuum hose trick works great for isolating both vacuum and exhaust leaks just put one end up to your ear and take the other end around the gaskets and fittings. If you have good oil pressure the timing gears are probably fine sounds more like a vacuum issue to me. GL

 

[lrdg]

Thanks Guys! It’s a truck again!

I changed out the module. It could be that I didn’t hook up the condenser, but I ran out of daylight and it will have to wait until tomorrow to check that.

Or, it could be that the truck fairies came and fixed whatever the truck gnomes have done to by BII. Either way it seems to be running a whole lot more like it should

Thanks Again!