SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: NoRestraint on June 02, 2012, 07:52:41 PM
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Pretty sure I have a stock 454, maybe a cam in it. What should the timing be around idle and 2500 and 4000 RPm? Appreciate it guys
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To give you a complete answer more details on your distributer would be helpful. GM, MSD or other. Vacum or mechanical advance or locked out at full advance. Most have set timing with full advance in around 3,000 Rpm with that being somewhere between 32-38 degrees total. Every engine is different and will perform best with varying amounts of advance. Are you familiar with reading spark plugs electrode to determine advance setting? Suggest you start at 32 degrees at 3,000 Rpm and add 2 degrees at a time until you do not see improvement in performance. At that point move it back to last best performance setting.
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First off, if it has a vacuum advance, lock it out and toss it....
Basic timing on a jet is virtually irrelevant. Basically low enough to get it to start hot (I like 15*BTDC)..Timing should be "all in" by 2500 RPM, so anything above that is not necessary.
On most of the BBC's I have worked on, the sweet spot seems to be from about 34* to 38* BTDC at or above 2500 RPM.
A jet boat engine runs like no other, your not trying to "pull a gear" with a jet, they draw little to no HP at the lower RPM ranges.
Most mechanical advances do between 12 to 15* mechanical advance, which is more than adequate.
Hope this answers your question... :-\
GT
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Not familiar with checking plugs for advance...but ill try the starting at 32 idea.... GT how do i lock the vacuum? I currently have the advance hose off the distributor and plugged to the carb so the secondaries are always running but top rpm is around 4 still
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Not familiar with checking plugs for advance...but ill try the starting at 32 idea.... GT how do i lock the vacuum? I currently have the advance hose off the distributor and plugged to the carb so the secondaries are always running but top rpm is around 4 still
You first....What does this mean? :-\
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Ok you know the hose that connects the distributor to the carb for the vacuum secondaries? My mechanic told me to pull the end off the dizzy and shove a screw in the hose so there is always a vacuum which would keep the secondaries on at all times? Hes built cars his whole life also so i trusted him. Is this kinda screwy? Haha
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Ok you know the hose that connects the distributor to the carb for the vacuum secondaries? My mechanic told me to pull the end off the dizzy and shove a screw in the hose so there is always a vacuum which would keep the secondaries on at all times? Hes built cars his whole life also so i trusted him. Is this kinda screwy? Haha
Yeah........Gonna say I call complete and total BS. Sorry.
The hose that would go from the carburetor to the vacuum pot on the distributor is what's called "port" vacuum. This means the vacuum signal is only present at certain conditions.
By plugging it you did the right thing, but it has little to do with the secondaries. The vacuum source for the secondaries (providing you have a vacuum secondary carburetor) comes from a different source.
By removing the hose from the distributor you have essentially locked out the vacuum advance. Steps can be taken to do a more sano job, but lets get her running first.
Here is a shade tree cheat. on your harmonic balancer there should be a hash mark for timing. Also there would be a timing tab with hashes and numbers on them. Using some Liquid Paper (aka White Out) align the hash mark with the highest number on the tab and make a mark on the balancer at the "0" mark of the tab. If it was at say 12*, you just marked it for 12* advanced, do it again with the new mark at 12* and it will be 24*, do it once more and you have 36*. You don't need an advance timing light to check for advanced timing anymore. 8) Just use the new mark(s) you just made.
I call it a redneck timing tape. :sly:
The secondary deal is another can o worms....If it is a Holley vacuum secondary, you should have a yellow spring in the diaphragm housing.
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alright finally getting around to this, going outside to do it now. I'll let you know how it goes haha. btw is checking for TDC ok to do with a screwdriver? I don't have any fancy tools :banghead:
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alright finally getting around to this, going outside to do it now. I'll let you know how it goes haha. btw is checking for TDC ok to do with a screwdriver? I don't have any fancy tools :banghead:
i wouldnt put anything metal into the spark plug hole. rubber hose, a piece of speaker wire... nothing that could break off, nothing that could scratch or damage anything.