Cafe Racer Forum banner

1 - 20 of 22 Posts

·
Registered
Joined
·
97 Posts
Discussion Starter #1
But I've got something stumping me on the simplest engine I have ever worked on. Ok, I know she's no cafe racer but my newest Cushman has me pulling my hair out. It's a flathead air cooled dirt simple engine. I cannot get it to suck gas up the intake to the cylinder. The engine is brand new (I had the local Cushman expert build it because it was cheaper than the machine shop work would have been for me). If I put my hand on the intake port it seems to suck. I took the head off and the valves seem to be sealing. The valve lash is right. The intake is clear of any restrictions. When I bolt the carb and intake on to it it blows gas out into the air filter, and nothing gets to the combustion chamber. Do any of you have any ideas what could be going on here? I'm at my wit's end. Oh and it ran kinda good for one year and then in the spring this happened. It's getting cold so I pulled her out to see what the hell's going on and am stumped. Again I know it's not a cafe, but we did hotrod it somewhat. we tossed the huge alligator body and built a nice light one out of 1/2" coldroll. We also added a jockey shift to the 2 speed "transmission".

 

·
Premium Member
Joined
·
11,267 Posts
Well, in most cases, if a four stroke engine was doing that I'd say the cam timing was way off.

As far as it "seems to suck" when you hold your hand over the port...depends on what you mean by "Seems". When I build an engine you can hold your hand over the intake, crank it over and it will damn near suck your hand into the port...and it will hold the vacuum for at least 20 seconds. I mean you KNOW it's sucking.

My first suspect would be the exhaust valve leaking, second head gasket, third valve oil seals (assuming it has any), fourth would be cam timing...assuming you didn't already check it.

Be very afraid of engines other people build, about half the people doing it "professionally" don't seem to know what they are doing.

BTW...more pics of the machine please...looks cool.
JohnnyB



Edited by - jbranson on Nov 10 2007 05:20:07 AM
 

·
Registered
Joined
·
353 Posts
I always liked Cushmans but I cannot for the life of me figure out why the're so expensive.

Branson's on the right track, it sounds like - check compression first, if it's waaaaay off then pull the head & see if the valves look good.
 

·
Registered
Joined
·
2,670 Posts
Some old Briggs had a crankcase vent thingy that went to the carb. It was supposed to be a one-way valve. If it didn't seal right it'd cause similar problems. I don't know if your Cushman has anything like that.

Otherwise what Branson said.
 

·
Registered
Joined
·
97 Posts
Discussion Starter #5
Thanks for the advice. I'll check out the cam timing tomorrow. I forgot to mention in the first post that compression is perfect, and the valves seal great. I even re-lapped them to be sure. I couldn't find many good pics of my red Cushman, but here are a few pics for you to enjoy.


Cushmans are cheap when you pull them out of a dumpster. The best part was the guy who put it there caught me taking it and gave me the title.



Same bike as the last pic. I was so happy to have done my first restoration. I also had my first brush with the law that day. Good thing the cops were more interested in the scoot than the fact that I was 13.



It's all about aerodynamics. (first day on the one that won't run anymore)



The stable a while ago, we have added a few since this pic was taken. Damn I need to clean the garage!

Thanks again for the advice. Cam timing makes sense. I have to get it running so I can swap out carbs. The old tillotsons are junk. I just need to get one thing figured before I introduce a whole new set of variables.
 

·
Premium Member
Joined
·
11,267 Posts
I could see myself riding around in South Florida on one of those in the 60's. Neat machines, probably dead reliable when they are "right".
JohnnyB
 

·
Registered
Joined
·
97 Posts
Discussion Starter #9
Here you go. No she only has a 360 for the time being. I have a lot of other stuff to upgrade before she is ready for big block power. And I had a nice little 360 with no miles on it when I started this project. The 73 is the year of the dart, and I'm from 83.

 

·
Premium Member
Joined
·
11,267 Posts
When I was a kid driving my 68 GTO there were three vehicles I wouldn't race. A pickup truck, a vette, or a 340 Dodge Dart. Some of the Mopar goodies available back then for the 340 were outrageous.

Attached is a photo of the 383 in the Road Runner my brother and I built during our Mopar phase. I think this was taken right after shut down during a cam break-in. Headers still have a nice cherry red glow.
JohnnyB

 

·
Registered
Joined
·
97 Posts
Discussion Starter #11
That was probably a good rule you had. I won't race pickups anymore after I saw a kid take out the side of a buddy's car when it went sideways on him off the line. Dart's are great because they only weigh about 3200-3300 lbs with a smallblock. I dusted many people in my are back when I had a 318 auto with 2.71 gears in an open rear. As soon as I get a new Valve body for the trans I can't wait to get her out on the road again. She will have a 300-325 horse 360, manual valve body, 3.55 sure grip rear. The best part is that it looks like a bone stock 318 untill you take the air cleaner off. I'm even still shifting on the collumn. I bought it from a little old lady that had owned it since new. I did all the paint and body, and now I'm about done with the driveline(for now). I just wanted to a sleeper look with it to pay tribute to the old lady that took care of my car for mr for so long.
 

·
Premium Member
Joined
·
11,267 Posts
Yeah... I meant Duster...not Dart.

Something about the Dusters seemed right for drag racing, good weight transfer or something, maybe just the right rear suspension geometry, helps that they were around 400 lbs lighter than the average back then.

My favorite sleeper of all time belonged to a friend down in Florida. It was a rusty, ass dragging, clapped out looking 69 firebird with a LT1 350, Borg/Warner T-10, Hurst vertical gate, and a 3:55 Posi. Had rust baby moon hub caps, holes in the body etc. But engine, drive train and suspension was right. Saw him embarass a lot of people with it.
JohnnyB
 

·
Registered
Joined
·
13,809 Posts
i had an alum body t-10. with the same hurst. 3speed with the lockout. what a cool box. could put it in myself lying on my back in the driveway. did many times.

jc
 

·
Premium Member
Joined
·
11,267 Posts
This baby had the four speed "vertical gate" all you did was shift it front and back, no side to side...yeah with the reverse lock out. Cool and expensive piece of hardware back in the day.
JohnnyB
 

·
Registered
Joined
·
97 Posts
Discussion Starter #16
I prefer this acronym: Massively Over-Powered And Respected. Oh and my car is a Dart Sport(same car as a Duster or Demon). I guess too many people pissed and moaned about the Demon name, so they changed it to Dart Sport in '73. Kinda sucks because that badge change cuts the value hugely. Oh, well I still love my car and honestly don't care what it's worth to someone else because I have no plans of selling it.
 

·
Registered
Joined
·
13,809 Posts
ah...the "airplane" shifter. cuz it was like flying a plane we always said. no, this had the 2 finger puller lockout. it weighed probably about 50lbs. that tranny/motor ate u joints on a very regular basis. and 2 clutches before going with a hayes hd. ahhh.....the ole days. our bug had a hurst shifter. you pushed it down to get it into reverse.

j
 

·
Premium Member
Joined
·
11,267 Posts
Oh yeah, I know the shifter you are talking about. Even cooler looking...kinda like an old timey syringe pointed down.
JohnnyB
 

·
Registered
Joined
·
23,303 Posts
I have a His/Hers Shifter in my GTO. Looks cool and good for some solid positive shifts but it still a stock piece of equipment.
 

·
Premium Member
Joined
·
11,267 Posts
Yep, my 68 GTO has the same..."Hurst Dual Gate". Nice conversation piece...but with a properly built automatic you just leave it in drive and it should do the job.
JohnnyB
 
1 - 20 of 22 Posts
Top