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Discussion Starter #1
my 67 XR7 runs a bit rough. I have checked the timing, points played with the carb. It has ben like this for years since I had the engine rebuilt. I think they put a 3/4 rv cam in it. And I have never been able to get it to run truly sooth. it is 289 been bored out 30 over. any suggestion.
 

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When you say runs a bit rough, are you talking idle or down the road? Cam affects idle but it should smooth out down the road. Does it smooth out with an increase in RPM? Say about 1500 to 2000? Been a long time since I have heard reference to a 3/4 cam. But a 3/4 RV cam is kind of a combination of terms whereas when we referred to a 3/4 cam it was a general term for a mild lift to slightly rad grind. An RV cam was a torque grind and didn't affect idle lope much. But the terms were so generic it really doesn't say much. Anyway cam aside there are a couple of things that could have caused some rough idle after an engine rebuild. Vacuum leak is one that happens with more frequency than is known. And usually at the intake manifold. Put your hand over the carb and gradually choke off the air a bit. Does the idle change any? It should just slow a bit as you squeeze off the air but not change the smoothness. A quick and easy test for manifold leak is to pour water along the intake manifold where it meets the head. As you pour water moving from front to back do you hear a change in the idle? If none of these simple checks shows any inclination of a vacuum leak, then how certain are you the carb is well adjusted and working properly? Is there a friend or someone you can swap carbs with from a properly running car? If these are all okay and the idle smooths out as you increase idle RPM then one can maybe attribute it to the cam. Oh one more thing, is getting it to a mechanic that knows how to use a vacuum gauge and how to read what it says. Some indicators from that can point you in a direction. But a cam that bumps can show some vacuum probs. In the end diagnosing a "runs a bit rough" on a car that has done it for years can be extremely challenging. If it runs fine otherwise with no drive-ability issues, maybe just keep driving.
 

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Most likely it has a cam that uses the 351W firing order. You aren't using the 289 firing order are you?
 

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As was said buy letsroll, check all of your vacuum hoses . I had a rough idle and thought I had checked them all but looked again and found some that were cracked
 

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Can you post a video of the car running, and/or get the actual specs on the cam that was installed?
 

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Discussion Starter #6
I believe I am using the 289 order. If I try the 351 will it cause any problems when i start it like valve damage or something.
 

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In addition to what was written: check pcv valve and hose, make sure vac ports on carb are either plugged or hooked up (try plugging all vac lines and see if idle improves, including the brake booster)., Then check fuel delivery (all rubber hose between carb and metal fuel line AND rubber hose from metal line on driver's side fender to fuel pump), then ignition (points, condenser, cap, spark plugs, etc.)
 

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A simple method to look for vacuum leaks is to take a can of carb cleaner and shoot it around areas where it's likely to be pulling in extra air like around the carb base, either ends of the vac hoses, etc. If the car stumbles at one of the test points you have found one. Also another good test is to slowly starve it by closing your hand over the carb - you should be able to kill it by closing it off. If you can't kill it, then you got a pretty substantial leak somewhere, or if it's hard to kill you have a small one. Some good starting points here, let's see what you find out.....
 

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I have had issues with the improper firing order.. It would be REALLY rough running on only 4 cylinders.
 
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