2550SX
Seaman Apprentice
- Joined
- Jul 10, 2020
- Messages
- 40
I have a 1992 Chaparral 2550sx with a 454. Serial OD717696 I
I bought the boat a few years back knowing it had a Webber square-bore carburetor that had some warm start issues. I was surprised to see that the square-bore Webber was mounted on a spread-bore manifold. This is consistent with the diagram in my mercrusiser manual for that year which tells me this is the original setup. I guess mercrusiser had a surplus of 454's from chevy built with spread-bore manifolds after Rochester went out of business and mercruisers fix was buying square-bore webbers and adaptors.
I bought a new 800 CFM marine 454 quadrajet and installed it directly to the manifold like it should be (no adapter) and it fires up cold and hot fine, idles fine, runs fine at low speeds in the primaries. With the engine at operating temperature I attempt to throttle up to get on plane and it bogs bad before getting up on plane. I loosened the setscrew for the clock spring on the air doors and tightened the clock spring about 1/4" turn to provide more resistance on the air doors hoping that would solve the bog but it made little or no difference. I tried another 1/4" turn, and the bog persists. Followed by another 1/4" turn and another until I exceeded the limits of the spring and broke the spring. The bog never went away. There was no bog last week with the old square-bore Webber so I do not think there are any underlying issues with the engine.
I have effectively solved the hard start condition and added a bog.
I ordered a new spring that will arrive this week and I want to try and figure this out. The vacuum break dampener is new and it seems to be working correctly. I am wondering if I need to bend that rod inward a touch to increase the dampening effect. I do not think that is right though.
Has anyone else experienced no change when adding resistance to the secondary doors through the clock spring to eliminate quadrabog? That always seemed to work on the G bodies from the 80's that I would occasionally work on. This is the first time it has not worked for me.
I am no mechanic but I pretend to be.
Any suggestions and personal experience from you folks is welcome.
Thanks in advance.
I bought the boat a few years back knowing it had a Webber square-bore carburetor that had some warm start issues. I was surprised to see that the square-bore Webber was mounted on a spread-bore manifold. This is consistent with the diagram in my mercrusiser manual for that year which tells me this is the original setup. I guess mercrusiser had a surplus of 454's from chevy built with spread-bore manifolds after Rochester went out of business and mercruisers fix was buying square-bore webbers and adaptors.
I bought a new 800 CFM marine 454 quadrajet and installed it directly to the manifold like it should be (no adapter) and it fires up cold and hot fine, idles fine, runs fine at low speeds in the primaries. With the engine at operating temperature I attempt to throttle up to get on plane and it bogs bad before getting up on plane. I loosened the setscrew for the clock spring on the air doors and tightened the clock spring about 1/4" turn to provide more resistance on the air doors hoping that would solve the bog but it made little or no difference. I tried another 1/4" turn, and the bog persists. Followed by another 1/4" turn and another until I exceeded the limits of the spring and broke the spring. The bog never went away. There was no bog last week with the old square-bore Webber so I do not think there are any underlying issues with the engine.
I have effectively solved the hard start condition and added a bog.
I ordered a new spring that will arrive this week and I want to try and figure this out. The vacuum break dampener is new and it seems to be working correctly. I am wondering if I need to bend that rod inward a touch to increase the dampening effect. I do not think that is right though.
Has anyone else experienced no change when adding resistance to the secondary doors through the clock spring to eliminate quadrabog? That always seemed to work on the G bodies from the 80's that I would occasionally work on. This is the first time it has not worked for me.
I am no mechanic but I pretend to be.
Any suggestions and personal experience from you folks is welcome.
Thanks in advance.